He's not allowed to growl or snap at you for looking in his mouth. I've got a way I'd fix that, but I don't have a way to explain it from here, and I'd hate to recommend it not knowing the dog.
Every dog I've had prior to Homer, I've just pried them open and shoved the pills in. Homer is a difficult patient too (only he panics and squirms away) but we've been able to get pills in him on occasion by just wrapping it in lunch meat.
Can you explain it in FReepmail?