I buy corral panels made for round pens whenever they go on sale or I find them used. I have traded horses/cows and hay for panels too. I love them because they're movable. I love the idea of the heavy wire cattle/sheep/hog panels and t posts. Lots of people around here use those and really like them. You can use pallets, just tie them together with hay twine. You can get all of that stuff for free. Just be sure to check for nails or splinters. I have a bunch of temporary panels made out of those cute picket fence panels that they sell at lowes and home depot. I bought brackets made to screw to gates and hang to a post, bolted them to the ends on the top and bottom, then bought long bolts with nuts and washers to pin them together like you would a metal round pen. I bought them to bring to the fair and other agricultural events. They're sturdy but light weight enough to move around easily. I like Paula's idea of a dressage arena and visual reference. If you use a lunge line, you do not need a rail. I scavenged traffic cones, painted them white, stenciled letters on them and stuck silk flowers in the top. You can tie white clothesline rope around them to create a visual barrier to work off of, like the fancy chains they put on the show arenas. You can also buy those inexpensive rolls of welded wire garden fence and hammer the cheap t or u posts in the ground to tie the fence to. I use zip ties for these kinds of things. You can just untie the wire from the posts and roll it back up to move it. This may not work to turn horses out in because the wire is flimsy. I have tried the electric fence that looks like volly ball netting. It was hard to put up, and as it stretched out, i had to add posts to it to fix the sagging, but it did keep the ponies in. You could move that around if you needed to.