4 month old chasing tail - Page 3

Dogs have OCD only extremely rarely. They do have obsessive behavior though ( not the same as disorder) .  Chasing tail is one such behavior ( not disorder). Such behavior is caused by stress conflict and frustration.
 It can also be caused by itching and or other medical condition. Check with your vet.  ( prolonged periods of being lacked up, boredom, loneliness, trying to get attention and so on),
 Some dogs and breeds  have genetic propensity to such behavior but (unless exceedingly rare OCD)  the behavior is  always learned and such learning must be curbed as described by me above. There may be other approaches . 
 for more read here:
http://www.petmd.com/dog/behavior/evr_dog_behavior_compulsive_disorder#.UktUJNK-ofh
 

At 4 months old he barely is old enough to have learned much but now is the time to get him firmly bonded with  you and work on his FOCUS abilities,.that requires you learning how to do that.

Glad you came now and ask...Focus is important and if you can determine how his drives are and zero in on his most heavy one use it for your advantage,

Many here can give you tips and links to read if you need

Yr