Many moons ago, I fell in love with Spirited Away, which was an app hider as well. However, it ceased development and upkeep, and no longer worked well with Yosemite. Hocus Focus, though, is a superb replacement! I've been using it for several hours, now, and it works great. I can even configure the time before an app hides on a per-app basis! How awesome is that!
Minus one half star for no help and no manual. If you want to prevent an app from hiding, merely drag the selector all the way to the left, for "zero" and it won't hide.