Your buck really needs to go into a dry stall or pen for day or two. Were you able to trim his feet good to expose the unhealthy tissue to oxygen? Iodine also helps along with the copper sulfate. He would also benefit from a long acting penicillin. Keep him in the dry, feet bathed with the copper sulfate two or three times, and up for a day or two and his lameness should resolve soon depending on severity. His pen needs to be dry and clean. Hopefully someone with more experience will chime in soon.
Also forgot to mention that foot scald is contagious, and it could spread to your other goats. Keep your other goats trimmed really well so that it will not be as easy for them to harbor the microorganism that causes foot rot. Keep him up until he is better, so that he won't be as likely to shed the microorganism into the pasture your other goats are in. It is worse in rainy, damp, hot weather. Southern states are worse about this type of thing. Once he is well, and as long as your other goats are not showing signs, it would be best to put them in another pasture away from the contaminated pasture for around two weeks, so that they won't pic it up again. Boer goats seem to be more inclined to getting this than other breeds. Some people suggest that some animals are more genetically predisposed than others for getting foot rot. If he gets to where he is getting it all the time and you have a hard time keeping him well, I would cull him.