I can tell when my gelding is getting dirty because he smells "cheesy." I can smell it when I groom him and sometimes riding him. I can never tell just by looking because his......you know, always looks clean, not crusty like other geldings I have had. It seems like all his smegma accumulates inside the sheath, not on the outside of the.... wee-wee.
So he can look clean, but have alot of gunk up in there.
And I swear, it seems like most horse owners around here never check for beans. Every gelding I have bought has had a huge bean, and when you ask if they have ever been cleaned, you just get a weird look from the former owner.
I also have a neighbor who's horse has a huge bean (I checked because I was riding him for a while and when I got back and unsaddled he was just dangling.) Well, anyway, it was almost the size of a golf ball, too big to get out easily and I told the owner and she just said, "well, he's peeing okay." Ugh, I'm sure he's still got it there.
And now I have a mare, and low-and-behold, the gunk between her teats looks and smells just like the gunk geldings get in their sheaths. Who knew!