Congrats on the fence, Bev! That's a big project and I remember well our fencing projects. What a relief when you are done, huh? Yes, my first Pyr Cara, was a huge digger so we placed big rocks (some were close to a foot in diameter) around the base of the fence where she liked to dig. Then whenever she started to dig there a rock would drop into the hole and block her access.
We were really at our wit's end trying to keep Cara inside the fence. It finally took electric wire strung along the top of the fence to discourage her from climbing over (6'-almost 7' in places) and rocks to keep her from digging under, but it worked great. Hopefully, you won't need such drastic measures with your pups. We haven't had such big problems through with either Halley, Sammy, Cassie or Daisy, so I don't think that it's the norm (at least I hope not to that extent). Cara's Dad was renowned for being able to open almost any chain link latch that the breeder tried, so I think that it was just in *her* mischievous genes.
I would watch them very closely at first though. I think that I'd put them into the garage or somewhere secure at bedtime or whenever you can't watch them closely until you know whether or not they're escape artists. Oh and if they aren't microchipped, that would be probably be a great investment.
I'm glad that your kitties like being indoor cats. That's great & they'll avoid all of the outdoor hazards that way, too. It sounds like everything is coming together nicely. I'll be crossing my fingers for you for a smooth transition this weekend. Let us know how it goes, ok?