hiya, our 4 yr old flat coat retriever has a histiocycloma on the underside of his earflap, and not wanting him to contaminate it,are there any ideas how to keep it clean and sterile?

Hiya
Do you mean a histiocytoma? Has it been removed?
My Flat Coats have had a few histiocytomas, generally on their feet/face, we have so far only removed one, which was on my boys lip. Bit tricky to keep that wound clean and dry! :-)
I am guessing if you have had it removed and it is stitched you shouldn't have to do much except ensure he has 'clean' walks (my boy is a fiend for mud) and don't let him scratch it...perhaps a buster collar if necessary?