As someone who has studied in Canada for more than a decade, I still find it hard, to be honest, to distinguish/differentiate certain sounds, such as "son" and "sun", "cob" and "cub", "cup" and "cop"..and so on. I have found these words particularly difficult to pronounce correctly. When I hear people say these words and most of the time with proper context, they are quite easily understood. Yet when it comes to my turn of talking, I sometimes have a slip of the tongue when it comes to saying these words. I would presume that this is not comfortable for most(if not all) non-natives as well. How can one improve his/her accuracy of speaking, with special attention paid to words aforementioned. Comments are highly valued.