Sounds like a great set up. Never thought of Llamas as guardian 'dogs', lolwe haven't had a problem with predators (only my old neighbor with altimeter ate my last flock but he's no longer with this world ) I have 3 black lab's they keep most things out. My neighbor in the back has lamas to he keeps them lose in the day time. The only thing I worry about is 2 egals that fly over every few days, but we are close to the Mississippi River and they are all ways with fish in there claws.
I can't think of what else you could do to make your coop more attractive. I bet it is nice and cool when the grape vines leaf out.