Your dog could definitely cause some trouble (or worse) if you don't socialize and train him to behave. Rat terriers were bred to be excellent little hunters and killers, so you will need to put some effort in training... or offer another job to keep his mind busy. I'm a strong believer in training because I just don't know if anyone can guarantee that the door or gate won't accidentally get left open one day. I taught my dogs the "leave it" command and it has worked well. Here are some links you may want to check out:
How did YOU train dogs to leave chickens alone
Terriers and chickens
How to chicken-proof your dog
Good luck starting your new chicken adventure!