Does it have to be a pretty plant? What about catnip?

It doesn't have to be pretty, but we have cats who get to go out on the deck supervised. The location of the windowbox is such that they're not allowed up there (there's a potential escape hatch up there). I wouldn't want to encourage them to climb up around the window box by putting catnip there. Why catnip...is it stomp-proof?

I don't know if it's stomp-proof, but we had some growing in our yard, and my husband would even weedeat it every other week or so, and it would still grow back. So I just thought it might be able to take some bird stomping too. I can see why you wouldn't want to plant it though if it's a place that's off limits to the cats.

Maybe you could grow another kind of mint that's not catnip? I have never grown any other kind of mint before, so I can't tell you if it's as tough or hardy as catnip.

There's not much that can survive constant bird tromping (I tried and tried to grow things under one set of feeders and finally gave up). I guess I'd suggest moving the windowbox...

Yarrow, Achillea millefolia, works pretty well for me most of the year. It does nearly disappear in mid-winter but comes back strong in spring. It likes a hot, sunny spot.