Dog urine can burn plants, leaving them to wither and die. If your dog has developed a habit of urinating on the same plants, you need to find a way to stop him.
Fence It Off
One of the most reliable ways to keep dogs away from your plants is fencing. Wood or steel-wire fencing is sturdy and customizable; a low-voltage electrified wire around the perimeter might suffice. You could consider invisible fencing, but you'll have to train your dog, he'll have to wear a special collar, and it won't deter neighborhood ramblers.
While commercial dog repellents require regular application, consider other methods to make your plants less appealing. Bitter or spicy smells such as cayenne pepper are effective home remedies. Sprinkle some cayenne around your plants, or try companion planting with strong-smelling plants. Rue repels dogs, cats and flies.
Provide an Alternative Spot
Dedicate one corner of your yard to doggie deeds, installing a pole or other large fixture for your dog to mark. Mulch, pea gravel or a similar substrate makes cleanup easy and gives dogs plenty of surfaces to sniff. Plant the border with butterfly bush, lavatera or other shrubbery to make a visual barrier. Lead your dog out to use the designated spot until he knows it's the right spot to do his business.
Consider making a dog-business area in a front corner of your yard to encourage neighborhood dog walkers to let their dogs urinate in that friendly zone and not on your prize plants. The collective smells from this communal dog latrine will inspire even roaming dogs to deposit their scent there as well.
Discourage Bad Behavior
While you can train your own dog not to urinate on your plants, roaming neighborhood dogs are a different challenge. Motion-activated sprinklers are an effective means of keeping wandering pooches from urinating on your plants. Some models use solar electricity and a 3-gallon reservoir, allowing you to position them where you want without tying up a hose or requiring complex installation. Such sprinklers can cover more than 1,900 square feet of garden; they burst into action when critters approach.
If All Else Fails
Selecting plants that can survive getting drenched in dog urine is a good idea around your property perimeter. Violas, columbine, lilac, ornamental grasses and a host of other plants are virtually urine proof. Make sure the border plants are not poisonous to dogs -- the ASPCA maintains a list of popular toxic and nontoxic plants on their website.