They will never develop wanderlust if you keep them in the house.

You want to see them sitting by the patio door looking out at the garden...

It's an interesting cultural difference between over here and over there when it comes to cats and the indoors/outdoors. In its rather different way, it's as deep as the thing about the right to bear arms. We can't get our heads round that one, and Americans, it seems, can't get their heads round the idea of a right of cats to roam free. They both seem pretty crazy concepts to the culture that doesn't see them as pretty inalienable. Even if it's not in the constitution we haven't got.

Fortunately our garden is pretty big, and the gardens adjoining it on the other sides are probably much more attractive than the noisy road, if a cat wants to leave it. At least that's been our experience with previous cats. There's always a danger, but we want to find ways of reducing it.

Bill D's idea with chicken wire sounds as if it might be worth trying. That and some kind of cat repellent sprayed along the fence area, perhaps...

As for birds, as I said, there are a fair number of neighbours cats who come in and look around, and the birds seem to cope pretty well with that, as they did with our previous cats. The little ones get up out of reach, and the big ones stride around looking scornful and a bit menacing.