I had a tendency to lift my head up to see where the ball is going and top the ball. This is particularly true when I have a difficult target or trying to avoid an obstacle.
Is there a tip that might help me become aware of this problem so that I can avoid it in the future?
@Russ Choyce - I suppose at the heart of the matter is whether you can actually time your "curiosity" in order and cause you head to pop up at that precise moment, or is something in the swing making this happen - as @Joshua Flynn is suggesting - even if seemingly only on these more difficult shots?
Have you taken any video of your swing? If not, I strongly suggest that you make it part of your routine as the camera never lies. Then if you'd like you can post your swing videos here in this area of the Forum for others in the community to review and offer their commentary.
Beyond this, you may wish to give some thought to the V1 Swing Video Analysis - an effective and inexpensive service that I highly recommend to everyone in the school. This enables me to put my eyes on your swing and offer some very specific observations and corrective action plans if applicable. I liken it to bringing your swing into the shop for a tune-up or minor repair. Scheduling one on a quarterly basis for preventive maintenance will do wonders for keeping things humming along nicely, and it's also a great tool for pinpointing and resolving any issues that arise. The process involves downloading the free V1 app and then submitting two videos to me through the app - one down-the-line (captured from your stance line, not the target line) and the other face-on. You'll find more information about the V1 Analysis halfway down this page on the Saguto.Golf site.
Tom