Figure out it's max size and plant like it's a full size bush and leave at least 6 inches between what will be a full size bush and the fence. That gives you some room to get in there with shears but keeps the space limited for animals to get in there.

You could just trim them from the other side of the fence. You still need to leave some room between them and the fence.

I agree with both @CPPgardener and @pepper23.

Trim the top and front from the garden side and the back from the other side of the fence.