PoE POEFOREVER builds

Hi all, POB here: Trickster peepee brand is feeling really good, a little bit squishy but not enough to make me sad. Still feels plenty beefy in non-uber content. I have a VERY specific question: I've linked Assasin's Mark to CoC, but find that I have one more gem slot that could be linked (currently just running cold snap). Any suggestions for what to plug in here? I don't care if it is a support or another skill to cast. Ideally I would like it to be something that either helps me feel tankier or helps with clear. My knowled