Hi, welcome to GoY, whips are very young trees, which usually have just a thin stem or trunk, once planted they will start to grow like any other tree, while they're thin and 'whippy' you will be able to bend them into almost any shape you want, if you tie them in, however rabbits will have a go at them, and the trunks will thicken up over the years, and become as thick as any other willow tree trunk of the same age.
Rabbits will eat almost anything, I once knew a chap who fed his pet rabbits rose prunings, and they weren't the thornless varieties either, they demolished them like lettuce leaves, Derek.

Thanks I think I wil give the idea a miss