If I know they're gonna do it, nair oos. Or FJ nair over it. Or crouch > d-smash on it (although I'm doubtful that this one is a good idea). Something like that. Sometimes I shoot a full set of needles and it clips him as he's coming up or down, which is kind of cool. Doesn't come up as often as the aerial-based stuff, though.
I've hit the nair between lasers before and I've always been curious as to why it sometimes works and sometimes doesn't. This answers a lot of questions.
If Falco is really unpredictable and I can't tell how he's coming up then I usually back off and respect him to not get hit by my OHKO aerials. I might try the needles thing, though, or try to get a weird approach angle from a platform or something if I think it'll work. He has a lot of good options from the ledge, though, so if he uses all of them effectively it can be really hard to exert pressure on him. So you gotta be creative, and systematic.