Merging two different parts

Hello! I have a question and I hope someone can help!

So I am trying to make a birthday present for my friend, it's a horse bottle opener. So I have an STL file of a horse, and an STL file of the bottle opener I want to use, and I want to make them one part. So basically I want to position the bottle opener in the horse model and then merge them so the bottle opener stays intact and the horse gets cut away. So I know this sounds weird or easy, but the problem is that the bottle opener model has a slot in it to insert a quarter. When I overlay the two models that hole fills in. So I need a way to maintain the bottle opener.

I hope this all makes sense, I have accesses to autodesk, meshmixer and a few other programs.

Thanks a ton for the help!

wouldn't it be easier to cut away the part of the horse before merging the two ?

That way the slot shouldn't get blocked.

Me I'd have the slot end coming out of the horses posterior :-)

Can you post a picture?
OpenSCAD or otherwise Blender are free tools that do a good job in CSG operations (adding, substracting and intersections)

I think I figured it out actually. I was making the project to hard on myself. Basically now I am just cutting a slot out of the horse to hold the quarter where I need it.

So the quarter will go under the lip of the bottle cap, and the head and neck will provide leverage on the rest of the bottle cap.

Now I just need to get my hole parameters right so the coin fits snugly and won't be sticking out so far that it bends under force.

Thanks for your help guys!