i work at boarding kennels and weve got a collie in at the moment who spins in circles chasing tail and has an extremly short tail!
can be due to bordem and attention seeking behaviour, hes learned that when he does it he get atention. we use product called bitter bite, just sprays on and tastes nasty. you could also try vicks vapour rub, or tabasco sauce (i used that to stop my dog chewing walls!!)
or, if it permits, try a water pistol everytime he does it. he shouldnt like this and will begin to associate tail chasing with being squirted.
hope some of these help!!