I must say I find it interesting that the fact this dog is not desexed is an issue. I have 5 dogs here not desexed and they're just fine, particularly now that the girls are desexed. What exactly concerns you ? I honestly don't understand the problem. Is it that you are scared of males escaping to hunt down intact females?
If that happens it only means your fencing is
inadequate and you shouldn't have dogs at all. I think this poor lady has enough to worry about without you getting on your soap box wanting her to desex this boy when she doesn't want that. Give the poor woman a break. I'd take on that dog in a heartbeat if I was there, just to set her mind at ease. Wouldn't even worry that he might want to kill the cats. My cats know to keep clear of our dogs.