How can you turn a rapid pulser on and off?
Just connect a switch to one of the wires. This will cause the wire to function as an OR gate, so the clock (or "pulser", as you call it) will only oscillate when the switch is off.
[Edit] By request, here are some example pictures:
However, the switch placement is irrelevant: you could place the switch literally anywhere in the circuit.
You can use this, I have tested it.
grey dot = switch
red dot = torch
yellow square = block