
This is how I teach it.
1. I assume you have the down perfected. If not you need this first.
2. Teach the flat command, so the dog knows to lay on it's side.
3. From the flat position. Put the treat to the dogs nose and bring it down between the front legs, the head should follow, then lift the treat over the chest and down the otherside of the chest to the floor, saying the 'rollover' command.
A bit difficult to put into words, but gradually build up the speed of going across the chest. Eventually you can do away with the flat (always a handy command to have up your sleeve, sure to impress the vet :) ) and then you will find you will not need the down. 'Rollover' alone should do it.
Be patient, not the easiest one for the dog to pick up. But this worked for me.
Good Luck
Sandra
ps Teach the dog on a soft surface like a quilt or soft carpet, it wont hurt the dogs backbone when it goes over slowly to start with.