I use an IKEA Billy bookcase to hold my filament rolls.  Sometimes some of them would roll off the self.  I made this parking block to prevent that from happening.  Four blocks cover the width of the shelf.  I used #4 by 5/8inch wood screws to attach them to the shelf.  

Included are a Fusion 360 and a STEP files so you can make changes to fit your situation.  

I printed mine with 0.2 layer height, 3 perimeters and 25% infill.