One thing I do is use a screen over the boil kettle while chilling the boiled wort. Just keeps out the critters as it cools down. During the boil, most bugs get pushed away by the heat of the boiling wort, or so it seems.
If you leave the lid on, just vent it a bit, so that the DMS can escape in the steam. No problem with up to 80% or so covered in my experience. Frankly, for me DMS problems now seem to come from post boil delays in chilling - like covering the kettle and not running through the counter flow chiller quickly enough (that mistake was made only once and a valuable lesson learned!)