Yay for a nice backyard! And I'm glad to hear that things are going smoother with the chihuahua. Like all good things, it just takes time…
I empathize with your need to find a good caretaker while you're away. In the past, I've had to be away for overseas research during summer months, but I'm lucky that the Doggy Daddy (my partner) is willing to stay behind. I think he's the only one that I would truly trust with the dogs, other than one other friend who unfortunately lives 10 hours away and already has a dog of her own. The other friends, eh, not so much. Even if they've grown up with dogs, none have ever lived with such a "difficult" breed.
So you're lucky that you at least have willing volunteers to start with! Since you're thinking in advance, perhaps you could screen/start "training" potential dogsitters. Invite them to spend as much time with you and Cody as you can possibly allow, so that they become just as familiar with, or at least aware of his quirks as you are, especially his potential to escape. I think, even if you prepare as thoroughly as you can, a little bit of worry still remains... I just try to remember that dogs are super adaptable, much more than humans sometimes. I would much rather leave my dogs in the care of a friend whom I trusted, rather than a "professional" kennel or dogsitter, because the stakes and sense of responsibility are different. And if you've done all you can beforehand, what else is there to do but worry? It'll work out...