There are so many things that could be said here in regard to the where to put the apostrophe but I'll restrain myself from telling you exactly where to stick it.You're welcome >>smile<<
Sadly, many native English speakers don't seem to know the difference between the contraction of "it is (or has)" and the possessive form of "it." Many people seem to think that "there, they're, and their" and "to, too, and two" are interchangeable as well. And I've noticed that people don't distinguish between "Yea!" (meaning "hurray") and "Yeah!" (meaning "yes") any more.
Oh yes, and accept vs. except, affect vs. effect, and loose vs. lose. There are actually quite a few more words people tend to misuse.
Should it be the ocean's tides, or the oceans' tides??
When I wrote "oceans' tides" on the board the students were convinced I made a mistake, thus prompting a quick lesson on possessive plurals.