I've read that it's better to park on the Spain side and walk in to avoid lines, but I also read to beware of thieves dressed as parking attendants on the Spain side who steal your car when you think they are parking it. Could anyone tell me where there is "secure" parking on the Spain side?

If making a special journey to see Gib, get the bus.
If you are thinking of seeing it in passing while touring, consider:
is it really worth it to see a row of tacky tourist shops?You can see the Rock & Africa without going there.Go to Tarifa.

I parked my rental car on the Spain side in a Parking garage. It's near the McDonalds and was not expensive (couple of dollars for many hours). It was safe. If you're worried about "valets", just don't hand your keys over to anyone.

I agree with zippo that there's not much to do in GIB. The only thing I found nice was the dirt cheap duty free alcohol.. Less than 1/2 price any airport duty free!

I drove onto Gib about 10 years ago. No problem driving on, but getting off-- they have huge lines of cars, searching everyone for bringing tax free stuff from Gib to Spain. Searching mostly the Spanish locals.

Gib was interesting, and worth a trip in my opinion. St. Michael's Caverns, WWII history, visiting the apes, and some of the views were breathtaking.

We parked on the Spain side and walked in. If I remember correctly, they had the meters where you pay a flat rate and a receipt comes out to put in your window. It's a very busy street, I can't see thieves stealing your car.

We drove to Gibraltar last year and parked outside. As long as you don't put anything valuable in your car, there probably isn't too much to worry about.

I agree with the previous posters - driving into Gibraltar is easy, getting out is very time-consuming (at least a 45 minute queue).