
First thing that comes to mind is that if you really mean a tiny brook is the only boundary to your garden you need a fence prob on your side if you don't want a constantly wet dog that will also escape and wander.
I wouldn't presume to advise on breeds except to say that Border Collies are marvellous dogs but do need to be kept mentally and physically exercised or they will find themselves things to do. They are really clever but this cleverness can lead to them learning bad habits just as easily as good although that applies to any dog not given the right direction.
Anne