IMHO, brandishing a weapon at him and demanding he "prone out" is a bit extreme, given that he's in the back yard and not actually in the house or some such. I would have been more inclined to hold my weapon somewhat behind and against my leg while we discussed just what exactly the hell he was doing there, and not actually covered him with the muzzle unless/until he demonstrated hostility. If he's not there for mischief, he'll be glad to wait while I phone the pool company to verify his credentials. If he's not supposed to be there, he'll either run away, which would be wise, or toward me, which would not be wise. But I see no need to scare the guy half to death and treat him like I'm initiating a felony stop when he's just made a silly mistake while coming to clean my pool. YMMV.