Loosen the weight, but leave the string attached.
How are your balls? I hope well, because now things will get even harder.
Take the shoelace pull it well behind your back, stretch those balls until they end up under your ass.
Now find a flat and hard surface, like a wooden chair, or the toilet with the lid closed can also fit.
Now sit down, sit on your balls, put your weight on it.
Do you like? To me a lot ... bounces a little if you can, crush them well.
Stay that way for at least 3 minutes, then start bouncing on it for another 2 minutes at least.
Your cock needs to stay hard!