You've probably seen the articles/posts about homemade Coyote Rollers or Roll Bars. I'm hear to tell you, I've heard from those that have attempted to use them, and I hope not to hear from others who have tried this, as the stories are extremely sad.
The basic premise of these is to string up a wire/cable along the top of your fence and insert pvc pipe thru that wire. The information I've read recommends using 4ft lengths of PVC. Which is what the "real" Coyote Roller lengths are.
What people are telling me is that they are unable to string the wire/cable taut enough to keep the home made PVC rollers from moving down when any weight is applied to them. This means that when an animal of any reasonable weight uses them for leverage (like a dog or coyote), the PVC falls downward and the animal is STILL ABLE to use the top of the fence to leverage to get over.
The real Coyote Rollers are made from strong Aluminum that never rust (so are the brackets) and they can support 250 pounds on center. This means they will NEVER dip or lower down when weight is applied to them. You can even get them powder coated so that they will seamlessly blend in with your fence.
You can "try" a cheaper, less visually appealing method, but why risk your dogs life on it? I don't know about you - but I will not risk the life of my dogs with an unattractive piece of PVC.