Question: Under what circumstances should a home protection spell be used/put in place? For instance, after first moving in? After unwelcome guests have left? After remodeling?
I recommend thoroughly cleansing (physically and energetically) the home and putting up a full shield and ward, including protection workings, as soon as you move into a dwelling. This is part of what I call psychic hygiene. It’s like installing the mundane security system, but it’s always armed. It should be one of the first things you do.
After remodeling, I would check the shields (which you should be doing fairly regularly anyway) to make sure they don’t need any repairs. After unwelcome guests leave, I’d cleanse the space thoroughly: a shield will not protect against crap you actually invite in; but that crap can be cleared away.
(see, folks, I do actually update my blog on occasion. :) )