put a fence up while you are out?
Background: neighbours moved into house at the back of ours just before Christmas. Gardens back onto each other and are separated by a crappy, wire fence. Neighbours have a dangerous dog which attacked another dog badly a few weeks ago, and barks and snarls at the fence if I so much as dare to hang my washing out. My youngest child will not set foot in our garden if he sees the dog out.
Their youngest child (I’d guess he’s around 3) also appears to have very little adult input during his day, and spends most of it wandering the garden on his own or out the front on his own - while that is sad and makes me feel sorry for him, it’s also not my job to parent someone else’s child when he’s trying to climb over the wire fence as soon as he sees another human and his mum is completely oblivious 
The fence is going up at some point anyway, but they seem to have been away a couple of days and we were planning on getting the proper fence we’ve bought up tomorrow. The only thing that makes me a bit nervous about doing it, is the man who lives there is a complete and utter arsehole (as aggressive as his dog!) who is likely to get all offended and kick off if we say we’ve put it up because of the dog 
Would you wait until they are back, and tell them you’re putting it up (our side!), or just get it done before they get back