Both of you are very right and level one sentries can take enemies unawares but if the enemy is a quick thinker he can easily destroy your sentry in seconds, while this is dangerous to do when on the defense, setting them up in strange locations while on the offense can be very affective as no defensive players expect a sentry gun. A spy can be very deadly too, the best way to take care of this is with your shotgun so you can get your sentry up and running before more enemies reach your location, also it isn't a problem if there is a teammate nearby as you can repair your sentry while the teammate blasts the spy.








