It's not a method talked about much, but it's very easy and effective for men with upright angled erections. I gained two inches in three years. By taking breaks to ensure your hardness stays high, it can be very safe.

(Warning: I'm a pornographer and well recognized for my dick photography, links are explicit)

Demonstration of hands only: https://www.redgifs.com/watch/ruralgrownarthropods

After a year of only using my hands, I progressed to using a ring and rope. The waist strap keeps the ring firmly against my body, and the loop around my ankle lets me control the pressure. By taking breaks, I can allow blood back into my erection, keeping it stiff enough to not get damaged. The idea here is to put all the force into the ligament only, and not modify the penis itself.

At the same time, I control my calories, lift weights, and do HIIT cardio. At 37 years old, my heart is stronger than ever, and it's not just my dick veins that bulge.

Link to using the ring:

https://www.redgifs.com/watch/khakiheavenlyharpseal

Kegel education: https://www.redgifs.com/watch/defensiveunrealisticgnatcatcher

Macro dick shot while using the ring: https://www.redgifs.com/watch/immensenimblehuman