My dd got Mickey crocs last year at WDW and wanted some Jibbitz for them, so we got her a couple. Within 2 hours, they were both g-o-n-e. So, we got them replaced (lovely cm at the store....btw) and I wouldn't let her put them in her shoes until I figured something out.
When we got home, I went to Home Depot and got these black plastic washers that are about an inch and a half diameter and are less than a dollar each. I put the washer inside the shoe and then put the Jibbitz through both the Mickey head and the washer.
It's been a year and dd wears her crocs a lot and we haven't lost any more!
I'm planning on heading back to get a few more before our trip this year just in case she wants more for her shoes.