Sally's . If you want something thicker just leave the cap off for an hour at a time til it thickens to the consistency you want. Some head cement I have seen at fly shops is very thick and some epoxies are also that way, better for building a head on a streamer. For locking thread after the tie I use Sally's also, thinned 50/50 with acetone. Hasn't failed so far. Also want to mention that you can trim the thread too short after the tie, not leaving enough for traction to hold it together. The same with chenille. Too short and it can be pulled free after several fish have the chance to chew on it. Some of my early mistakes. I apply the post tie sally with the needle bottle available through anywhere that sells tying supplies. Thicker stuff I have put on and manipulated with a toothpick if I wanted it heavier on one side than the other. A turner helps when there's a lot of stuff to dry and it wants to sag to one side.
Creativity is just intelligence fooling around