Rollers and floppy-top fences can work, but only if the predators step up and hang onto the top of the fence to go across.
It's important to understand that a low fence with a roller on top will *NOT* deterr a dog or coyote. Even if they leap up onto the top of the fence as they leap across. True, they will likely fall, but they will fall into the pasture, not away from it. Only if the fence is high and the coyote or dog is essentially leaping high and attempting to drag themselves over the fence can this work.
If you notice on the video at the web page he has the rollers on top of a 6' fence, and has the dog come on slow and attempt to leap up onto the fence. That's because this is the only way the unit can work and block a canine. If the fence was lower, the dog would leap over it. Either cleanly leap over it, or leap up and over. As well if the dog make a good running leap at that 6' fence, it would have a fair shot of still getting over it from inertia.
Climbing animals like coons and such generally have no trouble climbing over obsticals like this as they are stable on their hind legs, and work their way over.
Devices like this must be clean, dry, well lubricated and in good shape to function. Anything that lets them bind defeats them. Be it dirt, rust, snow, ice, dirt, branches, etc.