Stop in for a cup of coffee

Yesterday I was on the phone with my beloved cousin while she walked her small dog. Suddenly she starts yelling at someone, what happened was she walked past someones yard and their unleashed large dog attacked. The owners were outside but made a half assed effort to call the dog off.
My cousin picked up her dog and all I heard was her screaming at the owners and a few other choice words
My cousin is a not a big woman and she is very kind but she can turn it on in a second
The phone went dead and I was in a panic.....Were on opposites sides of the country
I immediately called her husband and he didnt pick up. My only next thought was to call police in her town.
She called back and was safe, her husband also called
Without going into detail, both myself and her husband told her to stay away from that property
However I want her to carry dog repellant and im going to send her a couple of canisters
So my question is whats the best type out there
Thanks