You can take rentals to mex.You have to fill out some extra paper work and its cost a little extra,you also SHOULD get the mex. insurance as well.(rentals can make the best pre runners

) But do know, most have GPS in them and will alert the rental company you took it to mex.
But truthfully, I would not go to mex right now,there is a large "turf war" going on right now. (mex messed up by taking out the previous "controllers") lots of kid napping and blood sheed right now. Id say you have a 80% chance of being ok, but the wrong turn might end you up in some trouble.
IF you really want to go to mex,for the food etc, I would suggest going to Tecate, as its very simple to get around in the town. La plactia is a good place to eat at. just rember, if the locals are eatting there you should be safe, if no one is thier and place next door is stacked.....stay a way.
Sea world, the zoo, barona race way,
http://www.baronaspeedway.com/index1.htm
http://www.baronadrags.com/
the USS midway,is pretty cool.
old town ....dont go hungry, $$$$$$ and if you do, have to get something to eat, stay away from "something coyote" (drawing a blank on the true name, but it has coyote in it)both times I have ate thier,I have gotten sick.And made for one "crappy" date once.
there is 4 or 5 local casino's as well
barona has the racing, Viejas has a factory outlet center and concerts.harrahs has the resort. Just google "san diego casinos"
The only food place I can think of off hand that's family friendly with good food across the menu and fair prices is.....its not the "ritz" by any means. But its clean and has good food.
Napoleon Pizza House - (619) 474-2888
619 National City Blvd National City CA, 91950
I hate telling someone about some place to eat, cause as soon as you do, it turns to crap or something happens etc
Balboa park, ummm Jr may get a showing of "same sex love", as its right on the border of hillcrest, and hillcrest is "gay town".
The Ruben H fleet center is pretty cool to kids.Even adults in the I max dome.
The "grand canyon tour", is pretty awsome.I have seen people puke in it, as its a trip in the dome.
http://www.rhfleet.org/
pacific beach, mission beach, and ocean beach are the every day people beaches.Mission beach has bellmount park, the roller coaster etc.
PB and OB good chance youll run across a few "hippies" here and there if you know what I mean.
Imperial Beach that runs along the border of mex, I would not swim in! After going skydiving and seeing that shit slick coming from mex.....
Lajolla, del mar,torrey pines is "rich man's land"
wind and sea,if you go there becarefull, breaks on the shore....think fred flinstone surfing in to tree.
fiesta island, you can rent jet ski's
just one thing, no alky of any type on any beach in san diego. straight to jail,empty your wallet before they let you go if caught.
scripps aquaruim....but dont drive a SUV/large truck there. Or someone will write/key nice slogans in to the paint.
http://aquarium.ucsd.edu/
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also check sdreader.com they have alot of coupons and stuff also that might help you find things to do etc.