[quote=@Natsu]
So you just trust the the person isn't being a dick and giving himself the luckiest rolls imaginable?
[/quote]

Use Roll20 wherein there are embedded rolls that players and the GM can see, or secret GM rolls that only the GM sees.

[quote=@Iatos]
Well each time you use the Giga Cannon you have to roll the Dice of doom.
If you fail the roll your weapon malfuncions and you explode into small bits of data. 
[/quote]
Or the DM doesn't give anyone Machinedramon.
And I do very much recomend something like roll20 where rolls are saved in a chat.