What is the counterplay to Rengar?

This might seem like a QQ type thread, which I guess in a way it is, but I'm genuinely asking this question because I have no idea. Last game was the perfect example of every lane losing, and that momentum coming bot lane and causing us to get rolled as well. Their team had a Rengar and I was playing Cait, so I had an "escape" or so I thought. Before 20 minutes we were pushed into the base and I was at the bottom inhib tower, farming. Rengar popped ult and jumped on me with a single jump and Q, insta death. I don't play Rengar so I don't know if there was anything else that happened, but that's what I saw.

So, what exactly is an adc supposed to do against a Rengar with 2 1/2 items finished that can instantly explode you regardless of how quickly I tried to net away? It almost felt like I would've died the same way if I stayed at spawn. That champion has always felt like an unbalanced assassin, but it feels worse now. Is there any actual way to protect yourself from that "burst" besides banning in draft?

/RantThing