One of the "cardinal rules" (yep, look it up) of horse training is that you don't ever want to tell a horse to attempt a move that ends up with them having less confidence rather than more.
So, when I'm introducing a horse to going over poles, the last thing I want to have happen, is for the horse to misjudge a step, land on a round pole and then slip and stumble. Yes, eventually that's bound to happen, but when I'm introducing a horse to trying something new for me, I try to set them up for a positive experience! I actually prefer square poles but this summer, Mike's crew pulled down a bunch of old fence and they were going to "toss" the lovely big round fence poles. Of course, I immediately "rescued" them from the trash pile to use for my trail training. First, we had to pull out any sharp bits of hardware that had been left behind. And then, they were just what I wanted.
They were nice and heavy but definitely round enough to roll (BAD), so I did what I've always done to "anchor them". I scrounged up some cinder blocks! I've been known to either run the ends of the poles through the blocks, or (if the pole is too big for that) I wedge the pole between 2 blocks to keep them in place. That means (potentially) heaving around 4 heavy cinder blocks for every pole! But you gotta do, what you gotta do!
Jack stepping over an "un-anchored pole"...but it's SQUARE!