The 'dares' and 'grins' parts are gramatically correct, but you are right about the comma.
To understand it, you'd need to be familiar with the motto of the SAS (as Chug points out). It doesn't really make sense unless you know the original motto on which it is based.
Obviously the SAS haven't taken offence from our modification, as our server room still has all the windows intact and the door hasn't been blown off. I'm sure that the mighty SAS are more than a little worried by the oddness here too!