I like to do this also, but only when the dog gets into the advance stages of heal (when he know what he's supposed to be doing and following your lead). I'll walk at a brisk pace with the dog at heal, then slow down a little.....just keep changing you pace. Also, I'll zig zag and go in circles, etc. I do this simply because when out in the field you don't walk in straight lines all of the time. If your dog will heal the whole time while doing these things then you know for sure that your dog fully understand the heal command.