[Ringo1]

Also, if Booger gets ticked off ~ he could really let little Mason have it. Some older dogs are inclined to take so much; then then will go off.

So I agree that you need to get Mason under control. I don't think that spanking or slapping will help either so I would not even try those. They will probably only fuel his aggressive tendencies.

Is Mason neutered? Sounds like he is being territorial in your house. You can start with picking up any high value toys or treats on the floor that he might be inclined to 'guard' or be possessive of. Same with food bowls. No food bowls down on the ground except at set mealtimes.

Lucy tends to get growly with my Westie when they are up on MY bed. Lucy thinks it is HER bed. The minute she does that - I put her on the ground.

With Mason, I might put him in another room for little while (not long) each time he snaps or growls at your older dog. This worked with Ringo who was not exactly thrilled when we first brought Lucy home. Like a little time out. He figured it out right away and quit growling or snapping at her every time she got close.

Hopefully, others will come on and have some advice as well.