OR, you can install a robocock:
A further method is to replace the two corpora cavernosa with inflatable penile implants. This is performed primarily as a therapeutic surgery for men suffering from complete impotence; an implanted pump in the groin or scrotum can be manipulated by hand to fill these cylinders from an implanted reservoir in order to achieve an erection. The replacement cylinders are normally sized to be direct replacements for the corpus cavernosa, but larger ones can be implanted.
One advantage to this surgery is that an erection can be created whenever desired, for as long as is desired and as firm as desired. The major negative to it is that this surgical procedure can never be reversed.