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.
Old dogs, particularly bitches, often leave a damp patch after they have been lying down - why, and what should you do ? Leakage of urine (or urinary incontinence) is quite a common problem for older dogs - especially bitches. The signs are 1  : There is a damp patch on bedding, or on the floor, after the dog has been lying down for some time.  The hair around the external genital region becomes soiled with urine.