I'm having a hard time adopting Strays in my test game right now, mostly because my Sims are asleep or at work when the Gnomes I have out summons one to the front door.
It also doesn't help that when my Sims are actually on the lot that their dog ends up barking at the stray and scares it off... :x
EDIT: I need to see if I can scold the dog for barking at strays next time this happens. I know I can scold it for barking at other Sims (and even when the TV is turned on and he gets freaked out by it), but I need to see if I can catch him barking at a stray to scold him next time...