The safe approach is a correctly designed cage and having the wife under it before the boar is let in. I overbuilt and tested this one so I know it won't fail under all his weight. She is safe in it and he quickly mounts. I am always right there with means to stop him if necessary, but it has never been an issue. As long as you stay back and let him fuck,its fine. By that, I don't recommend trying to guide him either. He will feel around and find her pussy and fuck it just fine on his own. The bigger the boar the better, but start out small.