[cejx]

Are there any plants/trees out there which are chook proof?

[joyfull]

trees are generally chicken proof (although some of my birds do roost in ours) and my chickens happily eat the fruit of our apples, plums and cherries. However my trees are well established, if you plant new ones you will have to protect the lower area as they will love the freshly dug up area and will damage the roots.
Under hedges where nothing grows the chickens will love this area for shelter and also to make dust baths so again if newly planted they will need protecting for a couple of years.