In Xcode 4.x press

⌥⌘R

(or click Menubar > Product > Scheme > Edit Scheme)

select the "Diagnostics" tab and click "Enable Zombie Objects":

This turns released objects into NSZombie instances that print console warnings when used again. This is a debugging aid that increases memory use (no object is really released) but improves error reporting.

A typical case is when you over-release an object and you don't know which one:

• With zombies: -[UITableView release]: message sent to deallocated instance
• Without zombies:

This Xcode setting is ignored when you archive the application for App Store submission. You don't need to touch anything before releasing your application.

Pressing ⌥⌘R is the same as selecting Product > Run while keeping the Alt key pressed.
Clicking the "Enable Zombie Objects" checkbox is the same as manually adding "NSZombieEnabled = YES" in the section "Environment Variables" of the tab Arguments.

As per Apple's documentation:

1. In the project navigator, select your project.
2. Select your target.
3. Select the "Build Phases" tab.
4. Open "Link Binaries With Libraries" expander.
5. Click the + button.
6. Select your framework.
7. (optional) Drag and drop the added framework to the "Frameworks" group.