My first "roundpen" was constructed a couple of years ago out of white electric tape and push-in electric fence posts. It was located in the center of my back field, which is basically an extension of my backyard. It worked really well for the horses that I had here at the time: a group of electric-fence-respecting-introverts. I used it frequently. When Cody (extrovert) arrived here just over a year ago, he managed to almost immediately walk through it (by then the electricity had grounded out) so I had to take it down and I've been missing it ever since..
My new roundpen is located on the site of the previous one. The site is more level than most parts of our farm and has a good base of gravel for drainage. Plus, it is in view of the house for safety. I decided that what I really wanted was a roundpen that could serve as both an enclosed training area and as a large, multipurpose play obstacle. I think that we have realized both goals!
The new Parelli-inspired roundpen is 60' in diameter with two openings for "gates." It is made of 4" round pressure-treated fence posts. To create it, my husband borrowed a tractor-powered fence post driver and put in 27 support posts. Next, he cut them off at 36" from the ground with a chain saw.
Next, we measured the distance from the center of each support post to the next, one at a time, and cut a rail to fit. He used guesswork to angle the ends just a bit to reduce the gap between each rail. He also cut away the bottom half of each rail to create notch to set on the post. We set the rails on the posts as we cut them to fit. Once we had them all in place, we screwed the ends each rail with two screws into its support post using 3" decking screws. We recessed each screw head a bit into the wood.
For the gates, I used two 10' lengths of green/white (highly visible to horses) yacht rope. I tied one end to a screw eye set into the support post on one side of the opening, and then fastened the other end to a stainless steel heavy duty snap. I didn't use a knot on the snap end, just threaded the rope though, but the fit is tight enough that it would slow a horse down, but give under pressure to prevent accidents. To close, I snap the rope to a second screw eye located on the opposite post.
The result is an amazingly useful training enclosure! The wooden rail is about 39" from the ground and is sturdy enough to mount from and to resist a horse running into it. It is low enough that a horse could jump it - if motivated enough. (And if they did, it would be a huge clue that I was pressuring the horse too much!!) The roundpen is located within a small field, so if a horse did decide to exit the roundpen, he would still be contained. It is ok that it is not perfectly level due to the prevalence of rock ridges beneath the site.
The roundpen can also be used as an obstacle for practicing Follow the Rail and other riding exercises. I can leave the gates open and be able to alternate between riding on the inside and the outside of the roundpen. I also have the freedom to alternate which gate we use, to prevent a horse having too much of a preference for a particular gate.
For footing, I intend to mix a load of sand with a load of free wood chip "mulch." I'm also planning to create a path around the outside of the roundpen with small gravels for better footing when muddy.
I just want to mention that my friend Michelle discovered an easy way to maintain an arena or ring: hook a "de-thatching rake" ($50 from Tractor Supply) to a 4-wheeler or riding mower and drag it around! (Kids will love to do this for you.)
Even the horses are enjoying our new playpen. I sure am thankful for my Mothers Day ring!
PS - Plastic barrels are available from some car washes. I got mine for $5 each for the large and $3 for the small. Plastic yellow trailer wheel chocks (Walmart $3 each, I think) help to keep the barrels in place!