I was having an interesting conversation with DarkOwls the other day and we wondered why the sticking charms that Sirius has on all his posters continue to work after his death, also the spells that the founders placed on Hogwarts are still active 1000ish years later, but the Petrificus Totalus charm the Dumbledore has on Harry stops working when the caster died. From what I gathered, Dumbledore's protections on Hogwarts were still active so why is it that some spells last but others fade after their caster dies?

We couldn't come up with a plausible answer, so I was wondering, does anyone have any theories on this?