Ok
tarpleyg, here is my 2 cents for a very simple solution to your problem. Just use a driveway alert to change the prop from a sound activated one to a motion activated prop. I have done this with all of my sound activated props (I have several) and it works great on every one. You just glue the speaker from the driveway alert receiver over the sound sensor of the prop. In reality the prop is still sound activated but the PIR in the driveway alert triggers the driveway alert receiver speaker that that in turn triggers the prop. So I guess it is sort of a fake motion sensor

. But it works like a motion sensor. It takes about an hour to hack the driveway alert to do this but it is very simple and works great. All you have to do is remove the speaker from the driveway alert receiver and extend the speaker with additional wiring. The extra wire will need to be long enough to reach from wherever you place the driveway alert receiver to the speaker where you attach it to the prop. By putting a 5 or 10 ohm resistor in the line from the driveway alert receiver to the speaker you do not hear the driveway alert chime but it still triggers the prop. Actually, I just did this with a skeleton cat that my wife bought from Home Depot. It is very similer to the Howling Wolf in that the can meows and the mouth moves when it is triggered. The driveway alerts I buy are from Harbor Freight and cost between $10 and $12 on sale. Hope this helps you a little.
PS I posted info on these driveway alerts a couple of years ago but in reviewing the post I actually didn't put a true tutorial on how to do it as this was simply an "out of the box" way to use the driveway alert. I now modify the alert somewhat by removing the speaker from the receiver case, adding a 5 or 10 ohm resister to the speaker wire, and extending the speaker from the case to the prop. I will try to get this done tonight and put a link here.