I feel your pain. I have been drinking up a bunch of my stock, but I once had approx 50 opened as well. I have had several corks go out on me.
I tip mine over every now and then to wet them. At least every time I pour from the bottle. It helps, but doesn't completely eliminate the risk.
Some of my whiskies (high end and some low end) came with synthetic corks I don't have to worry about. I keep a few extras of different sizes on hand as mentioned above, and replace them if a cork starts to break apart or crack.
I store the bottles upright, as continuous exposure to the whisky is not advised.