I favour using the words "Hurry up" when you want your dog to toilet -- the neighbours don't know what it means, and it's the first thing that comes to mind when you are standing outside at midnight or when it's raining. Make sure you say it in a happy voice and give your pup a food treat every time when he performs, and you should have no trouble with outside toiletting. It's also very handy to be able to tell your dog to toilet before you go for a car trip.
The best information on all aspects of positive dog training is Ian Dunbar's site
http://www.dogstardaily.com sorry I can't get this to appear to click into but you can google it.
cheers