House Training an Older Dog

With regards to housetraining an older dog, it can actually be easier to do this. Puppies do not have the physical capacity for "holding" on until they are 4 months old or so. Before that you are just doing damage control and trying to get the concept across to them. Older dogs, especially ones that have been kept outdoors in a kennel, will not want to go indoors because it doesn't feel right. Follow the same rules that you would with any other dog during housetraining: out after every meal, out after every rest, and out every two hours otherwise. Don't just put them out in the yard and expect them to do their business. Take them to a specified spot and wait with them until they do their business.
Take that opportunity to teach them a word to "go" to, if they don't already know one. And, when they go, outdoors: PRAISE THEM!

SUDDEN ONSET OF MARKING
There are several possible causes for a dog that suddenly starts marking (urinating) in the house.
First, rule out medical problems with your vet.
If you've just moved into a new house and your dog starts marking, it's probably trying to claim the house by marking.
It also helps to actually catch the dog in the act. You can then yell "NO" to distract it, and then take it outside. This works well for dogs that simply think its OK. You MUST catch it in the act, though, yelling at it after all's said and done will accomplish absolutely nothing.
Be sure to clean up that spot thoroughly with cleaners.
Remove and Clean Dog urine
For fresh urine: clean the spot with any good carpet shampoo.