@Switch Blayde
'putting their foots down'
It's "putting their foot down."
Let's play devil's advocate.
"putting the foot down" means to put one foot down, so now both feet are on the ground, giving a better stand.
If multiple people do this, why would "putting their foot down" be correct? Each of them puts his/her foot down, one foot each. Therefore "feet" would be misleading (not both feet!) but the singular "foot" implies it was a shared foot. "Putting their foots down" would describe it best.
This reminds me of a sketch by the late Bavarian comedian Karl Valentin, who argues over the correct name for Semmelknödel (German pronunciation: [ˈzɛml̩ˌknøːdl]). They are a kind of bread dumplings made from dried wheat bread rolls like Kaiser rolls, milk, and eggs. The name derives from southern Germany, where semmel means bread rolls and knödel refers to something that has been kneaded.
Valentin argues it must be Semmelnknödeln.
Semmeln is the plural of Semmel, Knödeln is the Bavarian plural of Knödel (the German plural is Knödel),
Valentin reasons: to make the dish you need more than one Semmel and you never make only one Knödel, therefore both plural!
HM.