I have a large yard but no two trees are close enough to set up a slackline. I've always thought about doing a deadman's anchor and finally decided to do it. Here is how I did it:
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Step 1: Pick Your Spot and Dig Out the Grass
Cut out the grass so you can replace it later.
Step 2: Start Digging
Dig about 3 or 4 feet across and a few feet down. If you live in southwest Missouri like I do than you will not enjoy this step. There are more rocks than dirt.
Step 3: Make It a "T"
Once you've dug the initial ditch, dig another one to make a "T." The second ditch won't be as deep and will get gradually shallower as it goes.
Step 4: Drop in Your 4x4 and Line
Put your line around the 4x4 and drop it in.
Step 5: Bury the 4x4.
Bury the 4x4 and fill the hole in. Pack it down as you go. It also helps to add water to get it nice and packed in.
Step 6: Replace Your Divots
Put your grass back!
Step 7: Plan the A-Frame
I've seen a few different ways to build the A-frame. This is what I did.
2x4x44" - 2 of these for the vertical pieces
2x4x48 - 1 for the base
4x4x5 - 2 for the middle spacers
4x4x10 - 1 for support between the vertical pieces
2x4x16 - 2 for the diagonal supports. - I actually don't know how long they are. I just cut them to where they'd fit.
1/2"x7" bolts - 2 for the varied heights.
Step 8: Build That Sucker
I used a ton of 2.5" wood screws.
Step 9: Now You're Ready to Slackline
Pick your height and start tightening. You'll have to adjust the A-Frame as you tighten. I've found that if it's leaning a bit backwards it works better.