We have had the locking carts since the store opened. What's funny is our store has three parking areas the guests use... the main lot in front of the store, a second lot that is mainly for a bank, and a parking garage underneath the store which is mainly for the restaurants near the garage, but also has stairs to Target. The stairs lead you outside and you have to walk like 100 feet to the main entrance.
Anyway our lock strip (It's on the concrete and is yellow with a picture of a cart in a "no" sign) is right before the door to the stairs so you often see carts abandoned at that strip. Guests hate it because they have to take their crap out and walk down the stairs or around the building (or get their car).
Although people do get away with them. We are by a few high rise apartment buildings. Years ago, I was reading the guest comments and one of them said "I am the manager of blah blah blah Apartments. I have spoken to management of your store on many occasions. If you do not come collect your 50 carts that are on my property, I will throw them in my dumpster."