The easiest way to overcome a stopped/sinking anchor is to change how you think about reaching anchor. Your sequence is probably something like: pull to anchor, stop (now the creep starts), find anchor, focus (aim), release. Once you stop it becomes very difficult to get things going in the right direction.
Instead, focus on the idea that while you reach your anchor you are only slowing down the pull. Once positive anchor is reached and you are focused on the target you simply continue pulling (building back tension) until the release happens. So, it becomes: pull to anchor, slow down pull, find positive anchor, keep pulling, focus (aim), pull until release, follow through.
Mentally, this all sounds easy but sometimes the body isn't doing what the mind thinks. For training I'd get a video camera, even a digital camera with vid mode, and film your self. You can see what you think is happening and what is really happening. Work on just that aspect until you see positive results at close range. Next, take the camera out while you actually try to hit stuff and repeat the process. See if you maintain the same results, it may take some time.
Another alternative would be to invest in a clicker. As a training tool it will teach you to reach a consistent draw length and how to pull through a shot correctly. Use one until you learn the correct feel of a positive, non-collapsing draw, than work at transferring those results without the use of a clicker.
Chris