If he was using an ENO tarp, that was probably the problem. crazy

But seriously, either using rings or a drip line keeps that from happening. Doesn't take much, you can use a shoelace. Or if you're intending to go out in a total deluge, take a larger tarp with doors on the ends.
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki