Talk to me about cock rings, I can get an erection, but it doesn't last that long.

This might sound funny, but will an 'o' ring do the job?

I guess you don't want it to be too tight? Or leave it on too long?

I guess you remove it before ejaculating?

I've never used a VED for erectile dysfunction. But my understanding is that you pump up to achieve an erection, and then slide on something like a thick rubber band. I don't think this is similar to a cock ring. But I know you leave the band on to hold the erection all the way through to ejaculation.