If a condom slips and unrolls while intercourse, leaving the base (thin ring) of the condom further than the base of the penis, could accidentally get in the whole condom? or does the "ring" prevent that?
Often, even when someone has just put it on, condoms won't sit right at the base of the penis. That's okay. Condoms are still effective, just as effective, when they move up a bit. But that is one reason why condoms aren't as effective at preventing infections like herpes that can be spread skin-to-skin as they are fluid-borne infections, because they often don't cover the whole surface area of the genitals.
Depending on the shape of someone's penis, a condom sliding up could make it easier for it to slide off, for sure. So, as a general rule, you do always want to be paying some attention to that a condom is still intact (just take a glance every now and then, you'll either see it or not, and if not, take a sec to check things out). If you find condoms do a lot of sliding around on you, you can also experiment with using both a slightly snugger (smaller) condom and a slightly larger one. Sometimes a lot of sliding around can be stopped by just adjusting for fit.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead
(Adding: I mean like, If the guy is kind of slightly losing erection, so condom start sliping forward and in the same way unrolling, leaving a lot of space in the condom, like "putting an already fully unrolled condom")
Just know that if and when someone loses an erection to the point the condom is getting considerably looser, they (or you, whoever) probably should withdraw the penis at that point. Condoms can't usually be as effective without an erection because they often won't be able to have the tether they need to stay put.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead
I see, so assuming that happened, the whole condom would got stuck inside the vagina, right? or the condom will come out of the vagina still on the penis?
Proper and effective condom use involves withdrawing from the vagina or anus if and when an erection goes buh-bye. That is because the condom can -- it sometimes won't, but it can and sometimes will -- slip off much more easily that way.
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead
A condom always can potentially slide off the penis and into the body part of another person it's inside of, yes. Condoms can slip off or break: both are always possibilities, though less likely when condoms are used properly.
(I did just notice you appear to have more than one account/handle here, which our guidelines make clear isn't okay. Which of two I am finding -- this one and hedjoss -- would you like me to shut down so you are only using one?)
Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has. - Margaret Mead