I guess the trust level with him and Casey is doin' just fine...
I seem to be the only one able to go into the backyard without scaring Peepers, as long as I stay in the garden area, and don't try to approach him. While I was weeding my garden, I heard this plaintive little "mew"...then nothing...then a few more little "mews". Turns out Peepers has an adorable little kitten meow--he was moving towards the back door, mewing at whoever was on the other side of the glass. I assumed it was Dave, but when I came back into the house (around the front way) I saw no one in the kitchen but Casey. She had been by the back door, watching for me, and keeping an eye on Peepers. So Peepers was meowing at Casey, in a very friendly, "Hi, how are you, I like you" sort of way. So they're just fine. Peepers forgives Casey for barking at him, and trying to herd him yesterday.
How sweet!