From what I know, different rescues require different 'prerequisites' in order to adopt. IMO a 4.5 foot fence IS too low :c. Ours is about the same height and my two can easily scale it. Adoption agencies do make exceptions (?). But their 'prerequisites' are usually to protect both you and your pup. I hope they make an exception for you and you figure out a way to keep your potential pup from hopping over.
A dog's smile is on his butt! c: