So here's a handy instructable showing a good method of making unique natural ornaments for your fish tank.
Step 1: Gathering Materials
So for this piece I just used some old wood I had spare from a previous tank. You could find your own wood from local shops and the general area but it will need to be soaked and cleaned for a while before being put in with fish.
I also used a piece of clear Perspex and stainless steel screws in this build.
Step 2: Trial and Error
So this is the fun part.... Basically just arrange the wood in a way that looks best. Takes a while to get it right but you'll know when it is. If its a natural look you want then the wood should all flow together without any conflicting pieces.
When you're happy with how it all looks the next step is to mount it to the Perspex. Secure the larger pieces first with the screws then jam the smaller bits in the little gaps. You can even drill into the big bits and stick the small branches into the holes. Basically whatever it takes to keep it in place.
Step 3: Trimming Up!
Now the woods in place you need to cut off as much as the Perspex as you can. The reason for this is so it does not restrict root growth in planted tanks like mine. If its just for a normal tank without plants then there's no need to trim off.
Step 4: Placing Into the Tank
So now everything is secured and trimmed up you can install your home made ornament into the fish tank. Once mine was in place I planted up the tank. I also attached small plants to the wood to create a super natural look.
Hope this was instructable....