I've taken my dog into Mexico
many times. You have to have all of the shots up to date and you have to get an international dog health
certificate (not the exact name, but close), it cost about 40 bucks at the vet. Make sure that the vet does everything according to the instructions with the certificate, it's your dog that's in jeopardy, not the vet's.
Never a problem except with the stupid US officials. Everyone in Mexico is really nice, the TSA people are the real jerks.
I spent 2 hours in LAX explaining that I am not an infamous international dog food
smuggler and that I bought the dog food
at Costco in California
and that I wasn't trying to turn a multi-billion dollar profit by smuggling Costco dog food back
into the US in my carry on luggage.
So you have to throw away most of the dog food before you re-enter the US but the amount in the dog's bowl is OK.
Never a problem driving, only when flying.
Dogs LOVE Mexico, lots more to smell on the streets down there and it's really nice for laying in the sun, same as for us. Dogs like street tacos too. And street cevice. And leftover shrimp or lobster. Even first-run shrimp & lobster is OK with dogs.
And lots of good dog beaches. Yeah, it's pertty good to be a civilized dog in Mexico.