The Ninja Course

We recently-ish moved to Urbandale, IA to save my wife from an unnecessary commute. At our old house, we had several large trees in the backyard that we used to set up some fun things for our kids. The new house was an upgrade in many ways, but we don’t have any trees, so we send a lot of our yard toys to live in a box with my in-laws.

If you don’t know this yet, my family is very active. We spend a lot of time outside running, hiking, riding bikes, skating, climbing, and pretty much any other verb you can think of. When COVID-19 hit and things started shutting down we, like many others, found ourselves in a bit of a pickle.

After about a week of sheer insanity, we deemed it necessary to bring the trampoline and other fun things back to life.

Solving the problem of no trees

Major kudos to my Father in-law for helping me out with this, I don’t have much of a background in “wrenching” so I tend to take a “test it out” approach to most things. That being said, building something that needs to support the weight of my kids and their friends required some advice and guidance from a guy who is very good at this kind of thing.

The Project:

Find a way to set four massive poles up in a way that allows us to configure and reconfigure various play items for different lengths, heights, and in different combinations.

For example – we may want to put the ninja line over the slack line to help the kids get used to the different grips.

Step 1: Figure out what size poles to use

This year my boys turned five and seven. They are what we’d call “sturdy” kids and what I mean by that is that the are both friggin’ tanks. Knowing that we wanted them to use this structure for as long as they want to use it, we knew we needed to think about height.

To establish above ground height, or usable height we first had to figure out how far into the ground we needed to get the poles to feel confident. Without doing a bunch of calculations, we ultimately determined that with concrete anchoring them in, and with the assumption that I could get them set mostly straight, four feet in would ensure enough stability to prevent shifting. Also counting on the ground having been frozen and compacted every year, adding stability as the kids and their friends get bigger.

We ended up with 14′ long poles with 6″x6″ for the length and width. Not easy to maneuver but my Father In-law is also a big/strong guy with a big van so we got them where they needed to be with some sweat and teamwork.

Step 2: Figure out where to dig

There’s a whole thing you need to do before you dig called, “Before You Dig”. You will be asked to answer some questions about why you’re digging and where you want to dig and they will send a team out to mark your yard to show where you’re likely to run into things like gas lines, water lines, or other lines that would be bad to cut.


Even with most utilities marked, I ran into random things like our sprinkler system, in ground rain spouts, and old telephone wires. I can’t imagine what I would have run into if I was just guessing.

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Step 3: Digging

If you have access to some sort of digging machine, use it. I used post diggers that were just long enough to hit the 4′ mark and it got harder as the handles got closer to the ground.

If you are using a post digger, take the time to focus on keeping it centered and level. You might be able to get away with a slight tilt, or adjust a bit once you’ve poured the concrete in BUT the straighter it is, the easier it will be to make sure it stays that way. This also helps if you’re planning to use the cardboard tubes to help shape the concrete around the post — which brings us to our next step.

Step 4: Set the posts

In retrospect, I wish I would have used wider cardboard tubes to allow for more concrete and more play while the posts were setting. I’ve tested this thing as a 205 lb adult and I’m fairly certain it’s not going to give much/at all but I would recommend planning to use a tube that has a diameter more than 2″ longer than the posts.

It’s worth noting that if you’re digging manually with something like a post digger you should try and make sure the diameter of your hole is pretty close to that of the tube to ensure a snug fit — so all the play happens with the post and concrete within the tube itself.

Once the tube is in the hole you can lift your posts in and then pour your concrete. Knowing that we were dealing with kids who were not going to handle waiting well, we went with concrete that set faster. You’ll mix the concrete in a bucket and then pour it into the tube.

The tube we used was fairly tight to the post which kept it straight but didn’t allow for as much concrete as I would have liked. If you’re using a tube that has a bigger diameter than the post you may have to level your post and check it a few times while it’s drying OR use something like rope or straps to keep it level while it dries.

Step 5: Fun time

Our setup consists of:

  1. A slackline
  2. A ninja line
  3. Two hammocks
  4. A DIY tree hammock that I made much much bigger and now functions as a trampoline
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I’ll probably write more things and you might just want to read those too.

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