Foot rot smells, so part of checking sheeps feet is to sniff them
The spray you want is variously called Terramycin foot spray, purple spray and blue spray. There are others.
As Stevehants says - you need to look first, but look with an open mind. Yes it could be scald, or footrot, or compacted mud pushed up between the cleats, or an overgrown hoof (needs to be seen from the underneath), a stone or splinter stuck in the hoof, or..............
Is there any way you can put some hard standing in your field? Permanently wet ground is not good for your sheep or their feet, given that they are arid climate creatures. Even a pile of rocks would give them somewhere dry to play and help wear down their feet the natural way.