I just ran across a post here that said not to exercise your puppy on hard pavement if you can avoid it. Well since everything is melting and all the trails in the parks are pretty mucky I have been walking Gunnar on the sidewalk for about 1 1/2 miles a day. Will this really harm his joints? Most of the time we are walking with my two children so the walk is pretty pokey. Also how much is too much for a puppy, he is very willing to go as far as we have went so far. I can't split the walks up to much, somedays I can fit in two but most we can only get in one. Is two miles to far for Gunnar? He is now 15 weeks and a GSD. Thanks!