I guess I'm pretty lucky. I have a 5-1/2 lb. Yorkie girl. I trained her to go outside and also to go on wee wee pads. I guess you can only do that with little dogs. So when the little miss sees a drop of rain or snow and refuses to go out (she's a princess) I don't bother and she goes into the bathroom and does her business on the wee wee pad. She will go in wet grass though.

I guess you just have to be a bit more stubborn and make them go.