No matter what the event might be, including sex, an enema before it calms the nerves and improves the chances of success. As to becoming as hard as a teenager with a rubber doll, for me it likely won't happen! Still, I keep trying and extend foreplay. My XYL is understanding and she tries but I still look like yesterday's praying rose. If nothing happens until the end, at least I had an enjoyable enema.
Think positively! This way, you won't impregnate her!