Well, as they say, the only way to be 100% risk free is to not have sex at all
But we know that is unrealistic and what a dull life it would be.
We have a no fluid bonding rule, with the exception of oral sex performed on a woman, providing the trust and proof of sexual health is present. We have this exception because I only have lesbian sex and a big part of this is oral... and GF does a lot of D/s play, where oral sex performed on her is part of a service. No intercourse without a condom, no blowjobs, no sharing toys.
However, oral sex on a woman is still a risk, so:
On top of the fluid bonding rule, we also have a rule that we see a clean bill of health from other partners *before* any kind of play happens. If I meet someone who thinks this is unnecessary, embarrassing or over-cautious, I do not really care. I'm not only responsible for myself; I'm responsible for my girlfriend and her husband, since she has unprotected sex with the both of us. So I don't take the risk.
Overall, I get tested every 6 months, or before each new partner; whichever is sooner.
If I've been with a partner and I think there's some kind of extra risk, I might get an extra test to err on the side of caution, but generally, it is as stated above.
Oh - and re: the question about anal sex being riskier for HIV in particular. It is my understanding that this is because anal sex carries more risk of tearing than vaginal sex, due to the delicate nature of the skin and erm... the strain of trying to ram a truncheon through a keyhole, if you catch my drift. ~grins~