Bag balm is good for a dogs feet, works on humans as well, I've taken to using more Palmer's Cocoa butter formula because I like the smell and it seems to last longer. Booties for the dogs feet are a lifesaver.

A friend related a story about a three day trip down some beaches in Florida. His dog had never had problem with its feet before but on the second day it started coming up lame. He thinks it had to do with all the salt water softening the pads and them being chewed up by the sharp bits of shell. He got the dog through the hike by keeping it on a leash, to keep it on drier areas, and improvising booties out of a spare set of socks, adhesive tape, and some light line.