There isn't a Monty Python film or sketch with "Release the hounds" in it.
You might consider "Now the first thing to do when you're being stalked by an ugly mob with redcurrants is to - release the tiger!" from the Self Defence against Fresh Fruit sketch.
Alternatively, Mr. Burns, from The Simpsons is rather keen on releasing hounds on people. You might have better luck with a Simpsons sound file.
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