For those of you that have cars without inside hood locks, how do you all keep your hood locked down to keep people off from under it?

A .308 at 100 yards usually works fine. Or, you can simply use a chain (or cable), and a padlock. Secure the chain to the hood and wrap it around the latch.

I found a bicycle chain lock (length of chain encased in vinyl) to be the perfect length, and used with a padlock on my '69. Run the chain through the gap between the hood pin and hood with equal lengths dangling. Then as you close the hood feed them down on either side of the hood latch until the hood is closed. Crawl underneath and the ends of the chain are just long enough to join with a padlock below the grille support. When locked down the hood can't be opened more than about an inch. This is on a '69 so other years may require something different.

used to eye bolts and chained it down

Did you see Wes Vann's tech article on making a hood lock?
http://www.chevelles.com/techref/ftecref25.html
Jeff

I am thinking about using these. They mount where the racing hood pins mounted and look similar except they secure your hood. They are chrome and look nice.

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=2076&prmenbr=361

Steve_69,

Those are the locks I have on my 65 El Camino in my signature. They work great and help to secure the corners of my fiberglass hood. Just don't use them without the stock center hood latch. If you forget to lock them, you'll be buying a new hood. Don't ask how I know this, it's not a good ending.