It's "would have," people. Would have...could have...should have....
There is no such thing as could of. Or would of. Or should of. Or...had to of.
Say it with me. Would have. Should have. Could have. Must have.
(Or, the acceptable slangy Farscape variant: could'a, would'a, should'a. :-)) Note, however, that the contraction includes the "a" from the word "have" -- nary a hint of the word "of."