Kopertox has worked for us in the past. It will stain a white calf green for a couple days though, and it might make some hair fall out, but it works well.
we use soap and water then put koppertox on. if they have it in between the hoof cut some strips of cloth and spray some koppertox on that and run it throuth then. the really helps get it all.
I've never found anything that works better on foot rot than Micotil. One shot and its gone almost always in a very short time. As other pointed out to me on this site, Micotil is dangerous to use (fatal to humans), so get your vet to do it if you don't have a chute you can really secure the calf with.