I just watched it as well and I would recommend buying sleeves. One color for one deck and another for the other or making a deck list for each player
Sure, sleeves are a good solution when you regularly play with only one other person. But they would not solve the problem if you play with many people. Deck list would work, but it seems very unpractical.
I was thinking of maybe marking the cards somehow... Although, I know it is a sacrilege...