I think he is still too young to let him have the run of the house. A year is about the time with most dogs that they "totally get it". But, my experience has been with different (larger) breeds. My 6 mo yorkie has been the most difficult dog for me to house train. She's having "oopes" as well. My problem is that I have 3 kids who tend to "forget" that she's out (they are supposed to put her back in the crate after 15 min or so).
I was away on a 1 week trip last month and Trixie was poopin' all over the house. Order returned when I did
I love the bell idea...I've been wanting to do that too. Sounds like he's got the idea that it's a "bell to play." So cute. Just keep crating awhile longer...it takes alot with a yorkie (as I'm finding too).