Securing them to the wood is the hardest part - and took some time and effort to master.
What I do is:
1. drill two 1/16" or 3/32" holes in the Back side of the skull - about 3/4" deep - below the antlers
2. Then I cut the heads off two nails - and drop them in the holes- so the sharp ends stick out about 1/4". Then I hold the nails in so that they dont fall out.
3. I center the antlers on the prepared board - and firmly PRESS the skull on to the board. The Nails leave 2 impressions of exactly where to drill through the board to line up the holes.
4. Then I use sheetrock screws of the proper length - and recess them in backside of the board. If I use the right length screws - I can screw them in really tight, and they are flush with the back of the board.
Thats it - I can do them pretty quick now after 20 years,
FH