Reply to Diode direction for arcade buttons

Hi, I'm about to do my arcade button mod to my vci 100 in the morning. I'm a bit stumped with the diode direction. Everyone including the guy in the shop that I bought the diodes from tells me that the diodes have to go on the live wire pointing towards the button so that the signal can't go back down the wire but in the video ean golden has the diodes on the ground / negative presumably pointing back down the wire. Does anyone know the proper way of doing this ?

Many thanks in advance
Ipm