But I'd caution against its use on Chows, especially older ones, who are notoriously reactive to many things. If there's a potential reaction to the vaccine, they'd be better off taking their chances. If you're in an extremely rural area, good luck finding a vet quick enough anyway.
In AZ I paid good $ to have people catch king snakes to keep the rattlers away. Get enough of those babies crawling around and you'll have neither rodents nor king snakes. Actually, they can keep away unwanted bi-pedal visitors too. Once I figured that out and even posted a sign at the end of my drive, people would telephone me to come after their captures but wouldn't bring them to me on a bet. I lived safely at the end of a 5-mile dirt road for 8 years, all 'alone' except for the dogs and horses and snakes etc and nobody ever bothered me a bit. Go figure. Fourteen years much the same in CA, same result.
Which reminds me, as an aside, that friends once urged me to take a camping trip with them to get away from it all. They lived in town. I asked them why I needed to go look at somebody else's trees. Don't worry, they took it well.