My experience is that I am more likely to get a UTI after very frequent sex over a short period of time, and with a larger partner. I have only ever had uncircumcised partners so I have no idea if this is contributory factor.

I would recomend good hygiene, peeing after sex, lubrication,drinking plenty of fluids, regular sex, and if you are going for a marathon session once in a while trying things other than penetration to ring the changes.