>Does anyone have other vent-securing ideas doing minimal damage to the
>mounted surface?
 
Well, my method may not count due to the "minimal damage" requirement (*g*),
BUT what I've done in my house is the following.  I picked up some little
"bracket" thingies at the hardware store.  I wish I knew the official name
for these, but they are small straight pieces of metal with holes in them
for screws (included with the package).  Found in the "fasteners" section
at Home Depot-type stores.  Not angle brackets or L-shaped, just a 3 inch
or so straight one.
 
I use two of them per vent and simply place the bracket over the corner of
the vent so that the end holes are hanging over onto the floor, mark the
spots for the screws with a pencil, drill my holes, and screw the bracket
down.  Repeat on diagonal corner of vent.  NO ONE is moving that sucker
now!  And if you need to clean down in there because *someone* pooped or
peed down the vent (sigh), it's easy enough to undo.  VERY weasel-proof
and not really unsightly.  Works on linoleum and carpet too - with carpet
you're attaching to the subfloor under the carpet - just drill carefully
right through the carpet.  But it does damage the hardwood or linoleum
floor (except for carpet - it's invisible when removed from carpet).  I
figure if we ever sell the house, I can fill in the holes with something
or the new owners can just figure we were insane. :-)
 
I can take a digital picture if it would help...
 
Good luck!
 
-Pam S.
[Posted in FML issue 3555]