Possible Possum gets his catchphrase, "It's possible, it's possible", from Deputy Dawg's frenemy, Muskie Muskrat, and one must assume that the folks at Terrytoons had Muskie in mind for a spinoff series.
However, in 1965, it was Possible who was the first spinoff from Deputy Dawg. Problem is, Possible's shorts, produced between 1965-8, aren't in general circulation, unlike a lot of other Terrytoons characters. Lionel Wilson performed all the voices, including the Don Messick-esque laugh of the bull, the villain of the piece in this 1966 short, "Harm Sweet Home":
As you could by the name of Macon Mouse, these shorts were set in Georgia, while Deputy Dawg & pals were further down south in Florida. Dandy Deal, unfortunately, deleted the closing credits.