You didn't say what is allowing the water to enter the garage. Is it because of negative slope towards the door? Is it because the door doesn't shut all the way, and water is splashing under it? Is it because you have gutters dumping water at the garage opening???
My point is that you might want to consider the cause first. It they can be mitigated, you may not have to do anything to the garage or the door. From what little you've said, I'd suspect that any type of seal or guard you use isn't the answer. Now the water will puddle in FRONT of the garage. In winter, it freezes; in summer, it's a haven for mosquitos, mold, moss, and who knows what else. Depending on what you have for a 'surface' in front of the garage door, if it's dirt, just re-grade. If the water is from gutters and downspouts, relocate them and/or channel the water AWAY from the garage. If you NEED gutters, get them. And assuming the garage isn't one that was built at the turn of the 20th century, I'm gonna assume that it was properly disigned but maybe not completely finished properly.
If you have more info to offer, I'm listening. My best to ya and hope this helps.
PS: (I'm out-of-town to see a Flyers vs. Bruins game this weekend in Boston. Others may follow-up but I, personally, won't be back until Monday ...) Go FLYERS!!!