Any barrier that they can't see through should be good, but make sure that they can't plow through whatever you put up, because they are a lot smarter than most people give them credit for. If they know that there is something on the other side, they might just try to break through, even if they can't see it. We solved this problem with a 6 foot privacy fence. (It currently stands about 3 feet off the ground, and we did not cut it.) It is buried underground, so it is much sturdier than it would be above ground. However you do it, have fun and be creative. Just remember, these guys will probably weigh over 100 pounds when they're adults, so make sure whatever you make can take a pounding. Good luck
menagerie