Is it ethical to use a pallet knife to put leaflets through letter boxes

perhaps even sharpened down the edges.
Yes you've guessed it, today was the first time in about 5 years that I have put leaflets out and some dangerous mutt managed to catch a finger as I put a leaflet through.
Why don't people who have dogs like this either have an external box or fit one of those cages on the inside of the door? Postman must dread delivering to that particular property.