yup, guide dogs are taught to poo and wee on request and also to poo while on a lead. Its not actually that difficult to do. My own dogs have access to the garden whenever they want but I have taught them request words so I can be sure that they will be comfortable when we go out in the car.
Quote:
"Dog control orders provide exemptions in particular cases for registered blind people, and for deaf people and for other people with disabilities who make use of trained assistance dogs. Anyone with any type of assistance dog is not subject to a Dog Control Order excluding dogs from specified land in respect of his or her assistance dog, and anyone other than a registered deaf person (whose disability will not prevent him or her from being aware of and removing dog faeces) is similarly exempt from a Dog Control Orders on the fouling of land."