Posted: 24/04/2015 at 12:47
I would try phlomis because the stems are quite thick and sharp and the flowers are around the stem and quite tough seed heads. Euphorbia because of the sap.
Have they been eating geraniums? I don't think they would suffer too much and they will flower again.
You could also try the small ornamental grasses, there shouldn't be anything for them to munch on there.