What is the best remedy to kill millipedes in garage?

  I have been dealing with an infestation of millipedes in my garage door area. I have applied Insectigone dust and it has proven to be very effective, however everyday I cleanup the dead millipedes and the next day I notice hundreds more dead. That means that they are coming out of cracks in the concrete that I haven't found yet. Once I find the source, I wonder what is the best remedy to kill them once and for all and not only control them with powder.