When I moved here 6 years ago, I drove down with my 3 dogs in my truck. I had gone through all of the requirements of getting their international health certificates a few days before the trip, and had everything available for the authorities. Do you know that NOONE EVER asked to see anything about the dogs! I even asked at the border, and they just ignored me. Of course, to be safe, you should go ahead and get the certificate from your dog's vet, and have it handy in case you are asked for it. Your vet will know what is needed. One thing to be aware of -- there aren't many hotels/motels in Mexico that will allow your dog(s) in the room. Mine had to stay in the truck, and I'm thankful it was the beginning of February and was cool, as our trip through Mexico included 3 nights in hotels, with my poor doggies stuck in the truck all night for 2 of them (the Best Western in Tamaulipas allowed them in the room).