>>1246558how much anal do you do, and are there any routines involved?
prostate play can require a lot of conditioning and depending on what he's already conditioned to it can be challenging.... ideally he's not used to cumming with things in his butt, that will allow you to train him to cum without touching his dick. That's assuming you want him to enjoy it and cum like a girl. ruining orgasms are probably better for punishment/denial.
another thing you can do to ensure success with the prostate stimulation is to keep him from cumming for days and days. usually around a week of chastity I start getting sensitive enough to have prostate orgasms. wait for two to make it extra successful, and take some days off the anal play before you get into it to maximize intensity. basically you want to set yourself up for success because the whole experience is mostly psychological. the feeling of total submission and futility is what will eventually set a sub off, which is kind of counter intuitive--focusing on the orgasm will make it impossible to achieve. further to the success strategy, spank him, tie him up, spit in his mouth, do everything you can to establish his mental submission.
I am partial to power exchange and submission more than denial and humiliation so this is mostly my own preference.