I suppose you mean General?
No, I believe that Napoleon is suggesting that the marshal is now vulnerable. Making an approach towards the marshal might come in the form of a combination 2 unknown pieces approach–one may be the spy. And, guarding his marshal with his colonel is a rather expensive proposition–two power pieces tied up doing nothing?
As for keeping the marshal undisclosed, this would definitely be a rather daring bit of play/misinformation, but it is highly risky. Watching this game, it becomes rather clear that EnderWiggin has created a huge problem for himself as the center lane activity begins to unfold. In any case, the primary mission of Ender, should he have chosen to keep his marshal a secret, would obviously be to find Max's general.
Ender's big mistake (as the game was played with marsh taking colo) was not making a full fledged attack with his marshal and colonel (he was up a colonel and could invest it to find the general or take out the other colonel). Instead, he go tangled up with unknown pieces and a potential spy trap. All of this would have been exposed had he entered immediately with the colonel and marshal.