I had the best luck doing just what you're doing, that is, drilling out from the bad spots until you get to good clean core material.

http://www.pearsonariel.org/discussi...3820#post13820

Sounding the decks for me was always sketchy, unless I was in a big bad spot, then there was no doubt it was a "thud".

With the drill method, you can isolate your repairs and just fix the sections that need it. It's a real pain to try and pull deck skins off that are NOT delaminated! No need to go overboard and cause yourself more work than is necessary.