Hair that’s attached to you goes under, but my understanding was that hairs that you have shed need to be removed.
I’ve never personally dunked in a mikvah, and I’m very far from an expert. This is a story a friend, who was a regular user of mikvahs, told me.
According to this site, you DO remove dentures before immersing. 
In the mikveh , you want nothing to separate you from the water. Therefore before entering the mikveh , we remove all clothing, all jewelry (even wedding rings) and all medical appliances (dentures, contact lenses, etc) as well as cosmetics and fingernail polish. We enter the mikveh the way we were born: naked.
I get the reasoning that goes with “naked as the day you were born,” but it’s not like the water goes in your mouth. 
I started researching IUDs and the mikveh, but got very bogged down in (to me) legality. (No disrespect to those who follow those rules.)
Seems like you should shave most of your hair and all of your pubic hair, if it’s meant to be “as the day you were born”.
Actually, it does; you’re supposed to leave your mouth open.
When I went in the mikvah, my mouth and eyes were not screwed tightly shut. You don’t open your mouth and take in water or open your eyes under water.
Make sure also to relax your eyes and mouth; water should not go in them, but they should not be clenched, and neither should your hands.
Wait. So you need to be buck-naked while getting baptized? Ignorance fought!
Now, do they still do those mass baptisms outdoors in creeks and rivers somewhere? 
I saw that in a Coen Bros film, but everyone was fully clothed:
For a Jewish ritual cleansing, yes.
Note that some Jews not only cleanse themselves in a mikvah, but will also cleanse a new pot before using it. Where the Bible says, “then wash in water” (Exodus 30:20, 40:12, Leviticus 6:21, 11:32, 14:8, 15:5, and many others) Jews interpret that to mean dunking in a mikvah. The typical times for people to dunk themselves, other than upon conversion, is when a woman is done with her period, or after a man has a wet dream.
I kinda assumed it was his own nutty idea.
The Wiki article linked to says he was an Essene, a Jewish sect a distant third behind the Pharisees and Sadducees. Josephus said they practiced among other things, daily immersion.
The Dead Sea Scrolls are held to be Essene texts by most scholars.
It seems reasonable to consider an IUD a medical appliance, no?
But this makes the IUD removal/replacement seem unlikely (isn’t it a medical procedure?).
You wouldn’t remove a pacemaker. I really think it’s because it’s an “external” thing that you “wear”, like dentures.
God will keep you alive. I’m sure of it.
I might have enough right stuff to get a medium asteroid. Not as big as Ceres or Vesta, sure. But one of those smaller ones like Sylvia or Victoria.
Maybe your planet can be near the planet of the Little Prince. That would be cool.
Yeah, you can’t remove your own IUD. It’s not like a tampon.
This whole section of the discussion was prompted by this post:
ISTM that a woman converting to the pretty-darned-orthodox Lubavitcher (Chabad) group would have had a thorough discussion with the Rebbe about birth control before the conversion, and he would have advised her. This group is not into birth control; they have big families, and have sex at a woman’s most fertile time. A woman member of this sect who regularly visited the mikvah monthly would not be using an IUD.
The question of the legitimacy of the conversion might have arisen if she had the IUD removed BEFORE the mikvah visit and discovered later there had been some residual bleeding. A woman visits the mikvah after her period and after seven days of absolutely no blood (which she checks with a tampon or white cloth). The reason for this is not the popular mis-conception (see what I did there? 
) about menstrual blood being “unclean,” but because anyone coming in contact with blood is ritually impure. It’s not a female thing. If y’all will recall, Jesus sent people off to see the priests if they came in contact with a corpse or after he healed them. These are deep waters (I just can’t help myself), and I suggest the curious read the following article, because the subject is really too much to go into here. Anyhoo, @puzzlegal’s person might have been concerned not over hair but over blood and that’s why she wanted to dunk again. That makes sense.
https://www.sun-sentinel.com/florida-jewish-journal/fl-jjps-torah-0422-20150421-story.html
No, it was definitely the IUD (or its “string”) and not blood. I assume this woman had her IUD pulled after she converted and married, because yes, it’s a very pro-baby sect. But all sorts of people (well, all sorts of Jews) choose to join Lubuvich, and they come from many different paths.
And of course she wasn’t technically converting to Judaism, as Lubuvitch proselytizes among people who were born Jews but aren’t observant. I’m not sure why I remember the conversation as being about a conversion, maybe it was just ritual cleansing to join the community.
(The guy who told me this also said the he used to dunk in a mikvah every morning after he became observant and before he was married and settled and had a job and stuff.)
Well, I’m stumped.
What I remember from high school theology class from the late 1980s, Catholics are perfectly fine with baptisms done by other faiths, as long as they follow the formula, which IIRC was “I baptize you in the name of the Father, the Son, and the Holy Spirit.”
Interestingly enough, I recall the big deal being that some denominations didn’t invoke the entire Trinity, which invalidated it. I don’t recall there being any question about the “I”, although I suppose it was assumed that it was the priest doing it, so he’d automatically do the “I” part, since it’s part of his role as the administrator of the sacraments.
And FWIW, I was baptized in a Baptist church- full immersion, etc… but it followed the formula to a T, so I figure it’s good.
That’s by Machiavelli, right? Great book!
“And here comes in the question whether it is better to be loved rather than feared, or feared rather than loved. And would the rose have preferred to be feared?"
Machiavelli wrote The Prince. His son, Machiavelli Jr. (“Little Machiavelli”) wrote The Little Prince.