I agree that walking machines are a necessary requirement, not many people are able to walk their dogs on the road.

Same with me, I am strong and can walk 4 at a time on the road if I had wanted, but because I live in an area not suitable for walking dogs (too many farm dogs about, rocky ground full of broken glass (from the local hoons drunken walk homes lol) plus when it rains the surface becomes very dangerous, as my area is predominantly clay, very slippery!) I just free gallop my dogs daily in my straight runs. When it's raining heavily or dogs have an injury that means they are not allowed to gallop, I put them on the walking machine for 15-20mins.

Hope you find the right walking machine that suits your dogs.. I do agree thought that a rubber belt is better than slats... slats can break more easily than rubber plus dogs seem to feel more comfortable on rubber.