I’m a male, and I’ve thought of wearing a Roman collar on occasion to deal with this occurrence, if it wouldn’t be blasphemy to wear it.
In my experience, if I would say, “I’m religious” or “contemplating the priesthood”, it makes the girl more want to seduce me/defile me/lure me away from purity/God/et c. than one would think (common-sense would state that to a secular girl, who would be making the advances, saying “I’m strongly religious” and quoting the Bible and/or a Saint with attribution would turn them away: I only had to do that once before I was disabused of the notion), probably in a way analogous to many women are not attracted to a single man, but immediately become flirtatious or seductive if they see 1) another woman with that man or 2) a wedding ring.
The method I eventually learned was a completely blank look on the face, combined with intentionally “not getting” innuendos, followed shortly by ceasing communication entirely while giving a short look that says, “what are you talking about? I don’t get it.” That, in my experience, generally elicits either 1) a sigh and frustrated walk-away of some sort, or 2) a statement to the meaning of, “are you human? do you know what ‘sex’ is?”, followed by a walk-away, or 3) a “that man must be a gay” followed by a walk-away (I’d much rather be thought of or imagined as a gay, than be known in actuality to be a fornicator, much less an adulterer).
I’m sure such techniques could be adapted to a female, although I’m not sure with the same level of effectiveness, as, generally, I have seen, the man is supposed to play the role of initiator and pursuer, and the woman is supposed to play a pre-scripted role of feigning lack of interest or lack of understanding, much in the same way I described myself behaving above, and the man continues, and the woman eventually relents (or states up-front “you’re not my type” with disgust, or, if a slut, has all of the equally-slutty men chasing her without deciding one way or the other).
Essentially, all I do is exude complete lack of understanding (naivete? or studied asexuality: more the latter, it being somewhat hard to describe in words alone, it depending so much on non-verbal communication) and/or not play the man’s pre-scripted role; as only the most forward women approach a man in the first place, it is surprisingly effective (because, even though these woman take the man’s role in “initiative” - I suppose as part of “female liberation” - they, likely to do with the essential character of female-ness, do not continue to play through the aggressor/pursuer role as most men would). As a man, as well, much I can do by controlling my environment: outside of “hooking-up” environments (drinking establishments, dancing floors, et c.; places that I do not frequent) I find there are few women of the type who approach a man as I describe: thus, the occurrence is quite rare (albeit not completely absent).
I digress before I begin an amateur sociological analysis of courtship and/or “hookings-up” and gender roles and the stereotypy of men, women, and the celibate or non-sexual.