You are your own worst enemy, so protect your comp. Want to avoid accidentally deleting or modifying a layer? Lock It! You can quickly lock a selected layer by pressing Cmd+L (Ctrl+L). But what if you change your mind? You can't use the same shortcut because locked layers cannot be selected. Here's what to do instead. Press Cmd+Shift+L (Ctrl+Shift+L) to Unlock All Layers .