sewing on buttons

[candy]

I finished my sweater and sewed on the buttons but I am not satisfied with the way it looks. I put a stay button on the back so it would not pull thru. I have a shank button for the outside and I put the yarn thru it and then put the yarn thru the stay button and then I crossed the ends over like you would tie your shoes. I crossed twice to make a knot and then cut real close to the knot. When I pulled on it the knots came undone. So I did it again and this time not cutting so close to the knot. But I don't like the look of the ends sticking out. Any suggestions? Thread would just pull thru so I used the yarn only pulling one ply out. Is there a neat and secure way of doing it? I have to sew buttons on the baby sweater I am doing now so I want to make sure when the mom to be receives the sweater it wont loose the buttons in the wash.