I had kept Ace away from Luke since Luke is so rough and tumble. Ace is finally old and big enough to be around Luke.

After twice trying to introduce Luke and Ace I saw there were going to be issues. 

I decided to try structured heel walks in an attempt to show them they both belong and who is the leader.

They both know heel very well so i placed both in heel and we have gone for longs walks.

I would have them do intermittent downs, and sits, petting them both at same time, correcting if they tried to break.

Has worked well. I was able to turn Luke, Ace, and Lexi loose and play together yesterday with no issues. 

I called all to me and praised occasionally to ensure there seemed to be no issues of resource guarding, the resource being me.

All looks good so far.

A neighbor's rat terrier getting through our fence did show me I need a much more solid recall under intense stimuli (not sure if they were in prey or territorial drive) for Luke, and Ace as both seem they will be dog aggressive if one comes into their territory.