no one the men can not control if they have an erection most of the time, it is a involuntary sypathetic and para sympathtic reaction . nerves get a signal and the blood vesels in the penis enlarge and fill up with blood this is what causes an erection. most my men friends tell me they can just think of a women and get an erection any time of day.
of course it has to be hard to penetrate the female for sexual activity and there fore leading to pro creation . after the man ejaculates the nerves switch jobs and constrict the blood vessels in the penis and lets the blood out. the chemicles released during male ejaculation causes relaxation of the smooth muscles and leaves the guy in what is called a refactory period where it wont get hard for a matter of time.
they use to argue that men could not be raped because even if he said no he was standing there with a hard on , but it cant be helped.\
be well and be hard