I grew up with Tom Ackerman who played offensive line for the Saints, Titans and Raiders in the 90's, up til his retirement in 02. He said there is almost NO WAY to juice and not get caught in the NFL today. The testing is random, and sooner or later everyone gets tested.
Apparently he follows the only rule of NFL steroids: deny, deny, deny. EVERY lineman in the NFL and at least 80% of the players other positions use steroids and/or HGH. If you want to claim otherwise, you're just being incredibly gullible.
You can ride on the genetics excuse all you want, but genetics won't explain how the human body can endure the abuse that the NFL exposes it to and to be able to continue playing for 20-24 weeks out of the year.