welsh terrier aggresstion

Question
We have a seven year old female neutered Scottie, a three year old neutered male Welsh terrier and a sixteen year old neutered male Dalmatian mix whom we adopted a year and a half ago. Initially the Welsh terrier got along well with the Dalmatian mix and would even initiate a "chase" game.  However, recently the Welsh terrier has attacked the Dalmatian mix on several different occasions for no apparent reason.  We have pulled the terrier off the Dalmatian, given him the devil, and held him down. The terrier is the alpha male and we have tried to reinforce this by feeding him first, taking his leash off first after walks, throwing a ball for him etc. The male terrier also sits on our laps which the other two dogs do not do. The Dalmatian is not aggressive towards the Welsh terrier at all. The terrier sometimes pounces on the female Scottie and she responds by pouncing back.  After a minute or less they quit by themselves without any interference from us. I'm not sure if the terrier thinks he is pouncing/playing with the Dalmatian in the same way he does with the Scottie but when he does, the Dalmatian, usually on his back, will bite the terrier back, and then things escalate.
All three dogs are in good health.
The terrier attacks on the Dalmatian seem to becoming more frequent. Do you have any suggestions/explanations?

Answer
Your Dalmation mix is elderly and (although you may not perceive it, these are subtle body signals) may be suffering from age related cognitive problems or subtle physiological inadequacies (hip related, arthritic problems, anything that may make him appear weak to the Terrier.)  You are PROMOTING this terrier; I understand you are doing this because you perceive him as higher ranking but, frankly, this is back firing.  You need to establish control of this dog ASAP.

First, institute a regimen of positive reinforcement training for the Terrier.  These dogs are SMART and he will catch on very quickly.  Go to ClickerTraining.com to obtain information; also, read Patricia McConnell Ph.D.'s work on problem dogs and read John Fisher's "Think Dog".  While training him to one solid behavior ("Sit" but use a unique word), which will take approximately 2 weeks for a strong, 100% reliable response, put a house tab (long lightweight nylon leash) on this dog and DO NOT TOLERATE any nonsense behavior.  Your Dalmation is showing CLEAR SIGNAL of submission (on his back) but your Terrier is NOT RESPONDING.  Whether this is part of his perception of the Dalmation's failing health and cognition does not matter.  This cannot be tolerated.  By holding the Terrier down, you may be inadvertently rewarding him (touch is a primary reinforcer) and confusing him (since he is doing the JOB you have DESIGNATED for him.)  "Split" him from the Dalmation when he demonstrates this behavior by walking between them, picking up the leash and backing him away from the Dalmation.  Do NOT address the Dalmation or even look at him; maintain eye contact with the Terrier until he is visibly calmer, then lead him away.  So far, your Scottie is holding his own; this may or may not continue.  This dominance behavior of the Terrier toward your other dogs is not to be tolerated: this is YOUR HOME, and he must learn to respect that.

Once he has obtained a perfect response (and reliable) to the command for "sit", put this dog on a Nothing In Life Is Free regimen for at least six months.  He must EARN everything FROM YOU: all food, going in/out, all interaction, etc.  Ignore both other dogs in this process (do not reward them or even pay attention to them when you are dealing with the Terrier.)  Continue to give this Terrier first feeding, first greeting, first attention, but ONLY after he EARNS it.  DO NOT allow him to sit on your lap or sleep in your bedroom.  If he jumps up, stand up abruptly with an "off" signal, make him "sit", then pet him peremptorily.  Keep your attention short but sweet.  Give him clear signs of consistent, fair leadership.