I use a condom during anal sex, but even then you can still catch something. Talking with friends, Anal Warts seem to still be an issue, HPV.
Sadly, I don't believe there is any way to realistically protect yourself with oral sex. In no way, would I ever be horny enough to suck a cock that is wrapped lol. I'm not even sure if there's a normal amount of men who could stay hard while getting sucked off and wearing a condom. Also, cutting a condom's tip, then cutting it length-wise, so it's in a rectangle, and placing that over the bootyhole to terrorize the fuck out of it with my tongue just seems like too much work and if it didn't look presentable and smell fresh I wouldn't eat it anyways.
It does drive me nuts though that most gay guys I've talked to in the leather scene are like, I'm on Prep I can take as many loads as I want. Before PREP was common, it drove me even MORE NUTS when guys would be like, "meh, it's just two pills a day" if they were to become positive for HIV. People can really be stupid.
Guess my final thoughts are, I treat cum like poison if I'm in a ho mood, don't do drugs (love poppers, but swear they're ruining my eyesight), and focus more on my fetishes that make me blow a load hard instead of just focusing on anal sex.