[whpalmer4]

It's pretty unlikely that you'll accidentally delete an item in the iOS apps. You might well accidentally complete one (check it off), though. What I find most useful for catching such mistakes is a perspective I call Completed (what an imagination, eh?) which shows items grouped by Completion date. It's pretty easy to spot the accident because it is the first one in the list if you realize your mistake at the time it happens, and reviewing the day's completed actions is a good cross check, too. I don't recall off the top of my head if this is one of the built-in perspectives that you can activate, but the support ninjas can help you activate it, including constructing it for you if it isn't, and you don't have a Mac.

One thing worth noting is that if you accidentally complete something, the best way to incomplete it is with the undo, not by unchecking the box. The reason is that if the item in question repeats, you'll get another copy of it — one was created at the time you accidentally completed it, and another will be created when you complete the uncompleted one. If you instead undo the accidental completion, the newly created one will be removed and events will unfold as intended. If this isn't possible (because you've done a bunch of other work since the accident) hunting down the new repeating action and deleting it plus unchecking the accidentally completed one will work also.