a dog roaming free should do the trick just for scaring purposes.

with i take it you mean scrub turkeys? you may have to litterally create a cage over you garden patch, and for the rest learn to live with them.

as for possums they can be kept out of the vege' patch by erecting a mesh wire fence (6' high) around the garden with a secure gate then run that flat sheet tin around the top on the outside of the fence mesh, this will stop them from climbing over the fence. make sure there are not trees hanging over the garden or they may simply just drop off the tree into the garden.

len