googled it ... yuck
horns ... you mean the keratin sheath with tissue left inside after pulling it off the bone or is bone still inside ?
If they're still attached to the skull,you can boil it and whack the base of the horn with a rubber or leather mallet all the way around ... and when you feel it wobble (and the sound the hammer strike makes will change) .. pull/twist it off. A pressure washer will remove the rest of the goo and tissue from the inside of the sheath (just be aware that if you're not careful, you'll get it in the face).
Dunno about maggots, but fire ants will chew/damage the keratin... and if you leave the skull on the mound too long, they'll even damage the bone. Not sure how the keratin would fare in the "juicy" environment of your gut bucket either.
If they were sawn off the skull and the bone is inside, you might lag screw a piece of 2x4 to the bone to "replace" the skull, but I don't know. It would have to be a really fat lag screw