Handling older dog aggression to puppies

Question
Hi,

I have a male labrador/corgi mix who is 12 years old.  I got two mixed large breed puppies earlier this year (their mother is pitbull/rotti and something else, sire unknown, but vet thinks it might be mastiff).  

One is male and the other female.  The male is the calmer/more sedate of the two, while the female tends to be a bit active.

I realised that the older dog didn't like when the puppies tried to lick his face or come near him in general.  I've noticed that he trembles when he sees them somethimes, so I think he might also be afraid.  I've kept them mostly separated except for when I can be with them.  

The older dog has displayed what seems to be aggression (or jealousy) towards them more than once, even the female puppy.  In the latest episode, I had been playing "fetch" with the older dog, (puppies don't quite understand the concept yet, but they stayed away from the older dog) about 15 minutes after I had stopped playing, the male puppy was walking past the older dog by about 7 feet and the older dog suddenly dashed and attacked the puppy who tried to run away but dropped to the ground and turned on his back (submissive posture) while yelping, but the big dog kept at him.  I intervened and the puppy ran away but the older dog kept chasing him down and I had to chase them down until I managed to grab the older dog - about 40 feet.  

Once I grabbed the older dog I locked him away so I could check the puppy.  The puppy had no puncture wounds, just saliva on his coat which is fairly typical of the older dog's attacks - no bites to puncture flesh.

I brought the older dog back outside and held on to his collar.  Whenever he seemed to be giving the puppies "the stare" I jerked his collar to break his focus.  I repeated it until he started to ignore the puppies and relax.

Can you recommend anything to reduce the aggresion in the older dog?  

Answer
"Aggression" can be a difficult thing to diagnose; many things can cause it, and it helps to know what is causing it in order to know how to address it.

I'm including a number of documents dealing with aggression, and some that deal with dog/dog interaction.  Hopefully some of the information will be of use to you.


http://www.marinhumanesociety.com/Behavior/Handouts/DifficultDog.pdf
http://www.marinhumanesociety.com/Behavior/Handouts/PossessionAggression.pdf
http://www.marinhumanesociety.com/Behavior/Handouts/Aggression.pdf
http://www.ddfl.org/behavior/dog-agg.pdf
http://www.marinhumanesociety.com/Behavior/Handouts/PreventingAggression.pdf

http://www.ddfl.org/behavior/canine-rivalry.pdf
http://www.marinhumanesociety.com/Behavior/Handouts/MultipleDogs.pdf
http://www.ddfl.org/behavior/dominance.pdf