It is called a condom and really reduces the chances of fathering a child.
As much as the pill does.
But guys do not want to use it.
If you really do not want to ever father a child you can get snipped.
If you want you can freeze your sperm so you can father a child in the future if you change your mind.
But once again guys do not want to do it.
They can’t, none of those fit the bill for the average man and condoms? Condoms have been around for almost 170 years and they never really caught on for a number of good reasons.
What we need is something easy, safe, and cheap, like a monthly patch at the least.