Some dogs burn more calories than others (nervous/hyper/ and so on) so need different diets.
Most white meat doesn't have enough fat content, so the above dogs need a fatty red meat diet.
You won't something that's going to brake if it gets caught round the dogs legs, something thats to strong will cut to the bone.
A brick line as already said but not the nylon tipe.
Heavy flinted ground will f##k up any dogs feet no matter what breed.
If your lucky it will just be the pads but on a bad day it might remove stoppers or worst still cut there hocks and wrists and drop toes because of cut tendons.
My advise would be avoid the place as you wouldn't run a dog on a field full of broken bottles...