That's odd your vet wouldn't want it out as leaving it in is known to spread and can kill them. It's basically a staph infection so I understand the desire to treat it with antibiotics, but it's not that hard, especially for a vet, to just get it out and avoid the antibiotics. There are literally thousands I bet here on BYC if you searched that have taken it out. The only other way to avoid it is when it's in its early stages, sometimes a drawing salve like PRID will pull it out in a couple of days.