Well-healed incision... do you use the hyphen or not, which is correct?
Well healed incision or well-healed incision ??

Personally I would use a hyphen.

A tip I was given (probably gramatically suspect) is to use the words you're considering hyphenating in isolation with the noun.

Does a 'well incision' sound right? Not really. How about a 'healed incision'? Sounds fine. As 'well' doesn't stand on its own with the noun, hyphenate the two words: 'well-healed incision'.