I have a 3d deer target with a detached head and neck area.  The head/neck have become loose and I would like to glue them on more permanently.
Anyone ever done this, and what glue would be good to use?

Good question.  I thought people used liquid nails.  The problem is there is like 20 different kinds of liquid nails.  I don't remember which one I used but it just bairly worked, but I was not gluing something heavy like a head on. My target was target was getting to where it was going to break in half if I did not do something.

I used automotive molding glue and it has held for close to 2 years.

Take a wire brush and lightly scratch both surfaces to be glued. Wet a paper towel and dampen both surfaces. Gorilla glue towards the center of one side. Don't over do the glue,it really expands. I like to tie a ratchet strap around ( front to back ) and pull it tight. I have around 20 3d targets and glue all of them. I can't stand when they seperate. Especially when your moving them. When you have to seperate them to replace a center I use a meat saw blade and just cut along the seam.
GLENN

I'll second Gorilla Glue !  

I used Liquid Nails in the past until I tried Gorilla glue. Gorilla glue has held the best.

Silicon caulk also works.  Good way to use up those half-filled tubes one has lying around the house.