The border traverses a variety of terrains, ranging from major urban areas to uninhabitable deserts. Approximately 350 million legal crossings occur annually, and is the most frequently crossed border in the world. The total length of the continental border is 1,954 miles (3,145 km).
Only a veterinarian will know what's wrong with your dog but usually stumbling, wobbling and falling down is associated with neurological problems, especially if there aren't any other signs. I would really take him to the vet as soon as you can.
If your dog seems fine but is experiencing recurrent bouts of diarrhea, it's time for a checkup. It's important to bring a sample of your dog's stool to your appointment, even if it's watery. Use a plastic baggie and shovel a bit in there to take with you.