Up until recently, I have been leaving my brew in the carboy for about 10-15 days or until clear after signs of active fermentation have stopped before bottling and now I am thinking about wanting to check SG a few times towards the end to make sure the beer is stable or maybe dry hopping. Both of these activities seem to be a potential point to introduce oxidation of my beer. What should I be doing to avoiding exposing the beer to too much air when I do this and getting the dreaded cardboard taste? I'm using a simple rubber stopper and a 2 bulb lock in a glass "water cooler" style carboy. In what steps am I at the most risk of spoiling the batch with too much air and how can I best prevent or lessen the chance of oxidation? Am I worrying too much or should I relax and have a homebrew?