I do not think that means what you think it means

I discovered the following absolutely fabulous grammatical error in a story summary today:

"[blahblahplotblah] ... in an attempt to improve his marriage's sex life."

His marriage is having sex with ... other marriages?

I really, really want to use this example in my next TPR course, when we talk about all sorts of misplaced modifiers and faulty comparisons and other things that make a sentence not say what it means, but somehow I don't think they'd go for it. I'm probably stuck with endless example sentences about Elvis and toupees instead. Le sigh.