Do your shelves look like this? After every class visit, I walked around the library straightening dozens of shelves that looked just like this.  Although the bookends had a cork bottom, it did little to prevent book slides after a few books had been removed. 

Here’s a hot tip I learned from my colleague and fellow librarian, Cathleen:  glue kitchen cupboard liner to the bookends. 

    
I used Elmer’s glue, and it worked just fine. 

 I am so fortunate to have Sandi, a parent volunteer, who took home countless bookends over the summer, and used a caulking gun to affix shelf liner to them all. 
This method works SO well to prevent slippage, that it is actually a little difficult to shift the books over when re-shelving.  That’s a trade-off I don’t mind at all.