[DS] Hidden Units and Recon by Fire

I had an idea for DSII pop into my head last night while drifting off to

sleep (a sure sign of severe mental problems), and haven't been able to 
check my rulebook yet, so before I make the suggestion, I was wondering
two 
things:

1. Can someone refresh my memory as to how hidden units get revealed in 
DSII?

2.  Can any vets out there comment on how Recon-by-fire works IRl to see
if 
my idea meshes with reality before I go further with it?

Thanks,

3B^2

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