During the day, my 3 year old boxer/Corso will bug me to let me know he needs out. At night he just goes on the carpet without letting us know. (I'm a light sleeper so I'd wake up if he bugged) How do I get him to tell us he needs to go out after we've gone to bed?
The best method I can think of that would certainly help with your problem is to isolate your dog sleeping area.
You can use a crate until your dog learns to alert you whenever he needs to use the bathroom. He may not think you will respond when you are asleep and this may be the reason he decides to pee on the carpet instead.
So, here is something you can try.
Have your dog sleep inside his crate. Place the crate near your bed so that you can hear your dog when he makes any noise to indicate that he needs to go out to potty.
When you hear him, immediately take him our and provide a treat reward.
To speed up the training process, you can intentionally play with him late at night, provide water, and pretend to sleep early. By doing this, you are certain that you dog will want to go potty, and you can practice this process every night.
After a while, you dog will learn that all he has to do is make noise and you will wake up to let him out.
Dogs do not want to pee/poo where they sleep. They instinctively want to go outside, therefore this isn't something we need to teach them. However, we do need to teach them how they can communicate with us.
Hopefully this helps, don't be discouraged. For a 3 year old dog, it may take a little bit of time before he learns.
In a similar vein to the other answer I would be locking the dog in a laundry or bathroom overnight, with a dog bed and a bowl of water.
Last thing before going to bed, take the dog out and first thing in the morning again. See how that goes. If the dog doesn't not pee in the laundry you can try the house again.
The other thing is to leave a door part way open (not viable for all climates or places) or use a doggy door (not always viable for renters). Make sure you train the dog to use the door during the day and then see how she goes at night.
Make a noise alarm. Put some loose change in two empty soda bottles and run a string between them. At night, when he ventures into the carpeted room he'll knock the bottles over and make noise. Then you can call him or otherwise interrupt him and take him out.
It isn't that hard to teach him to ring a bell when he want to go out. First teach targeting with a clicker. Start with him touching your hand with his nose, when he touches, then click & treat. Then have him ring a hanging bell by the door. Each time before you go out with him, ask him to ringing a bell. As soon as he does, celebrate and run outside with him. Withing a few days, the dog will ring the bell on his own.