No magnets for me.
When I have to make sure the person I am "detaining" is not going to get away I always use masking or duct tape.
Whatchya got against good ol zip ties Partner/Willis?  They're cop approved too.   Know an heir to the inventor. It was worth it, it could be that simple 

Ohh, and they got them @ harbor!  
Now, who's tried the "YELLOW" gluesticks? Not the cheap white ones....