[quote=@Ploxerdon]
I recall somebody in the series trying that, it doesn't work.
And he doesn't have one left regardless if he plays it smart.
[/quote]

'Obey me' is too vague a command to be ironclad, Servants can resist it if they want. All that happens is that they get a nerf to their abilities if they don't obey. 

A better command would be 'You will not harm your master'. Which would solve the immediate problem, though I doubt it would ensure that Roland bothers saving your butt if you get attacked by another servant.