Hi,

If your line is forming a belly during the drift, then you need to mend the line back "up stream" to prevent the fly pulling through the current (not always a bad thing, but it sounds like you want to prevent it).

So, cast your fly just upstream of you. Once the fly is straight across from you, lift the rod and place the line up stream. If you still have line in your hand, then you can "flick" this up stream as the fly drifts down the current. This will extend the drift as you let our more line above the fly.

Does that sound like it might solve the problem?

- Jeff