Potters as their own Secret Keepers?

[Arya]

No: HPFGUIDX 87009

Ok, it has just occurred to me...if Dumbledore was able to be the Secret 
Keeper for the Order and easily come and go about Grimmauld Place, then 
why couldn't either Lily or James have been the Secret Keeper for when they 
went into hiding?  

The whole story before OotP came out with Peter in hiding after he became 
SK, the bluff between Sirius and Peter to thrown someone off and the concept 
of locking a 'secret inside a single, living soul' had me believing that anyone 
living in a location kept secret under this charm would have to remain in this 
location and that the Secret Keeper would not be able to tell any other single 
person the secret of the charm, without breaking the charm.  After reading 
OotP, this obviously isn't true.  

True, it is an 'immensely complex spell' but still, you would think it would be 
common to use then if  it allows people to move in and out of the location 
freely and allows for anyone whom the secret keeper tells to be able to find 
the location.  It sounds excellent for warding wizarding homes and any place 
in general that one would only want those that they deem trustworthy to know 
about and find.  

So, again, my question is this--why did Lily or James not just be their own 
Secret Keeper?  Also-- what happens if a Secret Keeper is killed?  Ooh--since 
the secret is locking within the *soul*, what happens if a Dementor kisses that 
person and sucks out their soul?  

Okay, enough for tonight...
Arya