Here’s a tip to help with using apostrophes correctly when showing possession:
Just remember the phrase Attack of the Apostrophes. The “of the” in this phrase is the key to deciding where to stick the apostrophe.
First, rewrite your sentence in Noun1 of the Noun2 format.
tire of the car
litter box of the cat (one cat, one litter box)
litter box of the cats (multiple cats using the same litter box)
current of the rapids
Next, add the apostrophe to the end of Noun2
tire of the car’
litter box of the cat’
litter box of the cats’
current of the rapids’
Then remove the “of the”, add the s after the apostrophe (when the noun is singular), and switch to Noun2 Noun1 format.
cat’s litter box
cats’ litter box
rapids’ current (not rapid’s current which might be tempting to do)
Attack of the Apostrophes— I think this trick is the bee’s knees (or is it bees’ knees) and hope using it helps you too.