Hey, well there are a lot of good points in all these posts but I am sure you know what is best for your household.

Yes small dogs can be potty box trained. Chopper is both box trained and outside trained. He will use his box even when we are home during the day but will go out with me if I take the big dogs out. It is not hard work to train them, just the same as training them to go outside. And it does make it easier on both you and the dog when you have to leave the house for too long of a period.

Dogs cannot use the same boxes as cats, not just because they will eat the poo but because some dogs will eat the litter and this could cause an obstruction. They have dog litter but I find it more expensive then the pads. I use potty pads that I buy at Wal-Mart (32 pads for like $7) and just lay them in the bottom of the dog litter pan, change as necessary and yes they will tend to go next to it if the pads cleanliness does not meet their expectations. I use one to two pads a day (depends on how much outside time we spend). I flush the poos as soon as I see he has gone and I know that once he has piddled on his pad three times he will not - WILL NOT - use it again.

Good luck with whatever you decide. I am sure an older dog can be trained to use a box too, just may take patience because they might not understand at first why you are trying to make them go inside when they know they are suppose to go outside, but dogs are smart and I think given the guidance needed they will get the idea.