Memory Management: rules to always keep in mind

• Within a given block of code, the number of times you use copy, alloc and retain should equal the number of times you use release and autorelease.

• You only own objects you created using a method whose name begins with “alloc” or “new” or contains “copy” (for example, alloc, newObject, or mutableCopy), or if you send it a retain message.

• Implement a dealloc method to release the instance variables you own.

• You should never invoke dealloc directly (other than when you invoke super’s implementation in a custom dealloc method).

http://developer.apple.com/iphone/library/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmPractical.html