Plane ones.
or
Three skunks fighting over a pickle
First dog: My master calls me Furball. How about you?
Second Dog: My master calls me Sitboy
or
The owner got tired of the (w)hole business!
or
Because an undocumented worker has been living on his head for the past 2 decades!
or
Because there's no one else to wag it for him.
or
Stinker Bell.
or