Wandering may be a form of communication or a way of releasing stress for a person whose usual abilities are impaired. Over 60% of people with dementia will wander at some time. If wandering is a new behavior or if the person seems upset, consult their doctor.
Leaving a wanderer alone puts him at risk for injury or getting lost. Never lock the person in a house alone. Build a pool of friends, relatives, neighbors, and volunteers from community organizations to watch him or her occasionally and give you a break.
The wandering, itself, may be serving a purpose for him and giving him satisfaction. When a person has a disease affecting their brain function, behaviors we consider unusual may develop. They may forget what you told them or where they are within minutes, so you find that you have to repeat yourself over and over.