Unfortunateuly, there isn’t a way to be 100% sure you don’t develop a venous leakage, because it can be due to psychological factors.
"What Is Venous Leak?
If the veins in the penis cannot prevent blood from leaving the penis during an erection, an erection cannot be maintained. This condition is known as a venous leak. Venous leakage may occur with vascular disease, but it also can occur as a result of poor muscle relaxation of the penis. Difficulty with smooth muscle relaxation of the penis can occur with diabetes or with Peyronie’s disease, a condition that results in the buildup of scar tissue of the sheath (tunica albuginea) surrounding the erection tissue (corpora cavernosa). Venous leak also can occur when neurological diseases or high levels of anxiety are present because these conditions can prevent adequate smooth muscle relaxation."
Venous Leak, Vascular Disease, and Erectile Dysfunction
If you feel a strong anxiety towards PE, maybe you should avoid it, sincea you are perfectly in the average for size. On the other hand, as far as chances to develop venous leakage due to physical/mechanics causes, a cautious PE regimen presents less dangers than a sexual intercourse (my personal opinion). PE could actually prevents venous leakage, since some kind of PE (pumping at low pressures, gentle jelqs) are sometimes prescribed to those who suffers of this disease.