I also highly recommend the Slidelock rulers.
I use the SlideLock ruler too but I keep it on top of my ruler. It's the best safety insurance I can have for no rotary accidents. Worth every penny and then some to me.
Doesn't the Nexcare leave a sticky residue?
The Nexcare tape is see through so there is no need to take it off the ruler. I never have so don't know if it leaves a residue or not. I have some rulers the tape has been on the back for several years. No loose ends poking up and still see through. The tape is made for skin so I don't think it will hurt my rulers.