We just got back from a week in Coz, out of 20 dives saw 4 lionfish the whole week. Our DM caught the first one in a plastic bag (it was a baby), my daughter and I ran into another one a couple days later, couldn't catch it as it was bigger and it backed into a notch in some coral and we couldn't flush it. The last two were biggies, we ran into them by that big cement block towards the end of the Villa Blanca wall dive. They were in between the block and the sand build up behind it, we tried to flush them but the current was pretty strong that day, it was about all we could do just to hang onto something, much less try and kill a couple of fish. Candidly, given what I've read here, and what we heard from the DM's all week, I was surprised we didn't see more of them. And we were looking pretty actively.