I tend to get "primed" easily when getting rubbed down and my question is: How do I deal with my inevitable erection?
I have only gotten one erection while getting a massage and it was a very attractive massuese and she was rubbing my inner thigh right by my dick. And I got a chubby, not full on rager. I get monthly massages and have for 5 or 6 years.
Ask her to focus on your back and not your legs. say you prefer to lay face down. And then you can hide it.
If you do get one, don't say shite. she will likely ignore it.