Well while he's on your sever you can overwride his "playdemo", "viewdemo" etc commands... but he can also disconnect and view that demo... or you can alias his commands and he can't view the demo unless he restarts the game... but STILL can see it...
and also, if you manage to make the demo unviewable... how can YOU view it then ? =)
Best demo recording is through HLTV, placed on the same machine as the server, so that you see what the server sees... I think =)
out of curiosity, why would you want a player to not view it's own demos ? ... if a player cheated or something and you cought him... he will refuse to give that demo away, therefore results in ban
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