i'm really confused.

my vet said the humping won't stop after a neuter because he's too old. (3 yrs old) i gave him a very stern stop and pulled him away. he even had a 1 hour time out in the house. my fiance' says i need to give him a light smack on his bottom. i don't believe in smacking animals or people. it breaks their spirit. romeo is very stubborn. help.