Necessity is quite the motivator. I had placed a geocache in a well maintained grove in a nearby city park. It was a bit of log drilled to hold the cache and the end was sliced and a nail worked as the hinge to access the cache. My first version was "muggled", as they say, after about 3 months. I wasn't too upset about it because I wanted to replace it anyway with a more natural looking version. If I'd have paid more attention, I'd have realized that a local group regularly cleared the grove of debris. Version 2.0 lasted about the same. I decided I needed something that wouldn't look like it needed to be removed. I'd recently read about making bonsai pots from a mixture of peat, vermiculite, and cement, and realized I could probably adapt this to my needs.

Step 1: Materials and Tools

plastic wrap or newspaper

freezer bag

portland cement

base mix: compost, bark, wood chips, dirt, sand. Whatever is handy and blends well with the location

sphagnum moss

3/4' cpvc scrap. long enough to hold the cache

"bison" tube

neodymium magnet small enough to fit in either the pvc or bison

screw

screwdriver
thumbtacks

glue, I used carpenter's glue

water

Step 2: The Bison Tube

I put a little glue in the bottom of the bison tube, dropped in the magnet, and placed the bison tube on a flat piece of iron. This made it stand on end and kept the magnet stuck at the bottom. I used carpenter's glue because I was in a hurry. I probably should have used a cyano glue or an epoxy, but aside from drying time, it seems to want to hold.

Step 3: The Cubby

My plan was to put a magnet in the bison tube, and have it attracted some metal in the bottom of the cubby. I started with a piece of scrap 3/4" CPC. I cut it about a half inch longer than the bison tube. I stuck a bottle cap on the workbench and worked stainless screw I had laying around through it. I then taped the bottle cap to one end of the CPVC so the flat part of the screw was inside. I dropped the bison in and adjusted the screw so I could remove the bison, but it wasn't sticking out. Once I had it adjusted how I liked, I pulled out the bison. Then, I covered the open end with paper and wrapped tape around the edge of the pipe to hold it. The paper is so no concrete goes in the tube, but you can poke it out after the concrete is dry.

Step 4: Consider the Impact

Concrete is caustic wet, drys solid, and has a lot of potential to harm trees, property, etc. My plan was to build a mold around a particularly deep nook with wet newspaper and pack a pretty dry mix so it looked natural without actually touching the tree until it had dried completely. I was worried about the caustic cement leaching through and harming the tree, so I ended up using a piece of plastic wrap.

Step 5: The Mix

Most of what I read about making concrete pots suggested equal parts peat, perlite, and portland cement. I bought a 50ish pound bag of cement. I had some composted manure leftover from repotting and some sphagnum moss laying around so I figured I would use that instead. I was going to be working in a park with high traffic, so I wanted to everything prepped ahead of time. I mixed equal parts by volume of each into a Ziploc and mixed it using the bag to protect my hands from the cement. The moss really didn't want to mix. The other two ingredients kept sifting to the bottom. "Maybe it'll be better when I add the water", I thought. It wasn't. If I had to do it over again, I would keep the moss wet and separate until I was ready to "pour".

Step 6: Red Team Go!

My thought was, "If anyone asks, I'm making a mold for an art project."
I waited until about an hour until sunset (8:30 p.m.) and set out with my plastic wrap, Ziploc of mix, a water jug, and some extra dirt and moss. I brought a big enough piece of wrap to cover the area of the tree I was working and could cover the concrete while it dried. I used thumbtacks to lightly tack the plastic wrap in place. I then placed the CPVC tube so the paper side was against the plastic and angled down to prevent water collecting. I used a stick to angle it.

When I was satisfied, I added some water to the Ziploc and mixed. Added a little more and mixed again. The moss was dry and really, really didn't want to mix. I should have just waited for the moss to absorb the water, but I thought, "Oh, the moss needs more water to mix." I had a soupy mess in a Ziploc, plastic wrap tacked to a tree, while trying to look inconspicuous. I opened the Ziploc just enough to let water out and squeezed. It was pretty gray. I was sure all my precious cement was just pouring away. I worked it as squeezed it until it would hold it's shape somewhat. Think mud pie. The moss still wanted to stay on top.
This presented a problem because if I were to dump it out of the bag into the mold, the moss would be on bottom. This wouldn't really help camouflage the geocache. I pulled a handful of moss of the top, set it aside, poured the remainder into the mold, and packed the moss on top. Next time, I'd just keep the moss wet and separate until this point. I then used shaped the... mud pie? moss pie? into a natural looking shape. Worried about the concrete fitting too snugly into the bark and becoming stuck, I pulled the tacks and used the plastic wrap to slightly pull the concrete away from the bark. This is another reason it was important that the concrete not be too wet. It would just fill back in.

******
-"I gotta ask, what are you doing?"

Doh! I'd been so focused on my work that I didn't see the couple approach on the path. After straining the water out, I'd carefully waited until I had a good window to work without someone seeing. They'd jogged by earlier when I had the plastic wrap set and was waiting for them to pass to mix.
I paused, considering my story, and decided to just fess up.
"It's going to be a geocache." I replied, slightly embarrassed at both my nerdy hobby and being caught.
"Oh. Well, we won't tell anyone where it is." Well I guess we both got a good story to laugh about later.

******
I quickly covered the concrete with the excess plastic wrap, covered it with some dry grass, and left it to dry for 24 hours.

Step 7: Holy Cow, It Actually Worked!

The next evening, I came back out to check on it. It wasn't completely cured, but it was set enough to remove. I unwrapped it to see how it looked and thought it looked okay. The end of the CPVC with paper was exposed, so I used my finger to poke the paper. I wrapped it back up and let it set another day to finish curing. I didn't want it to dry too quickly and crack. The next day, I unwrapped it, tested the bison, and let it finish drying in the shade.
It came out much better than most of my prototypes usually do. It's been placed, found, and already given a favorite point! I think I'm going to mix up some of the moss paint to help it get a nice live colony established to finish the camouflage.

Thanks for reading. If you enjoyed the project, please vote for it!