The beaver could be a good situation, the pond edges should become
very thick. But you may wish to control that yourself if you know what I mean.

As far as a cover strip, Pines are about the best for the cover as you have already done. For a quick fix, if the field edges get enough light, corn, sorghum, or Biologic Biomass, can all get the job done in one season. You will need ALOT of Nitrogen to get the highest growth. Use Silage corn for screening, as it will grow 8 ft or more. Remember, The Nitrogen is the key for high growth.