disable program from executing twice

I have a few simple VB6 programs but 1 major program that I am needing to make sure it is never running twice.
For some reason randomly it will continue to run in the back ground and the when it is executed again it duplicates everything it is doing.
Also I have some techs that aren't the most efficient and tend to just start up the programs when they are already running.

so all I need is a way that when the program is ran it will check and make sure there is no other instance of it running in the back ground or anywhere.