Why not? There's no limitation on the number of wards one can put on a building. Even the Paranetters who are minor talents have learned how to build up a defense of multiple small Wards - and more powerful wizards have multiple Ward types with multiple different trigger conditions even. Harry is a good example of that. Essentially, the Landmine puts a single shift of power into an alarm Ward and the remaining shifts into the Landmine itself.
I would think so from the dresden books, but YS 276-277 (last paragraph of 276 spills over) reads:
By default, a ward lasts until the next sunrise
unless you add complexity to make it last longer,
which is explained in “Duration and Enhanced
Evocation” (page 265). In addition, any spells you
wish to include as part of the ward construct
add their complexity values directly onto the
ward. It must all be cast as one spell. If you want
a layered defense, you’ll have to spend a bit of
time setting it up.