2 Spindle Router

I am working on a router with two spindles each on their own vertical axis (z and w). Mostly the machine is used for carving two of something. But I would like to be able to turn on either one or both spindles. I was thinking that I could use some way to connect and disconnect each spindle to the M3 command. I don't need speed control, just on, off, and some kind of running at speed or fault fault to shut it down if something goes wrong.