What's considered critical or difficult to discover is a bit subjective, but:

It's easy to forget that alignment is important on some architectures (other than for performance reasons), so be careful when using placement new: https://www.securecoding.cert.org/confluence/display/cpluspl...

This may seem obvious, but even the C++ committee got this one wrong when they created auto_ptr (which has since been removed from the standard): https://www.securecoding.cert.org/confluence/display/cpluspl...

This one is totally obvious but has a stunning number of ways you can fail to adhere to it, some of which look reasonable at first blush: https://www.securecoding.cert.org/confluence/display/cpluspl...