The monkey repellent, if it works, will work like a burglar alarm: turned off when people are around & on when away, so babies and people shouldn't be an issue. Dogs shouldn't be in the garden, but if they are, and they don't like the sound, presumably they'll also move away. But I would monitor it to see if it is having a bad effect. I already have CCTV on the garden to check on the monkeys.
The pulsed noise suggestion makes sense; it shouldn't be difficult to add.
I'm going to give it a shot and see if the monkeys react. My other concern is blowing out the tweeter - I have no idea how far I should drive it, but I'll start small and work my way up.