Trying to pair a yellow watchman

[Shoreliner11]

I've had a yellow watchman goby for almost 2 years now. He/she is doing very well and right now is my only fish due to a downsize in tanks. What method should I use in order to try and sex another yellow watchman? To my knowledge there aren't any physical differences but is there a certain method as far as introducing the fish to try and see if they are the same sex? Thanks
Aaron