Yup. You can't block stupid. All you can do is reduce the odds of bad stuff happening. Length coding like Mr. Pierce points out. Color coding helps, with red being positive and black being ground (or 'earth' for you guys on the other side of the pond). Also, for some items, connectors with shapes that can only be connected one way, work well. Some circuits such as external power receptacles have a relay wired into them that will not close if reverse polarity power is connected. This is especially important when some one tries to jump start your airplane with a car and clamp type power cables.
Did you have a specific circuit that you feel needs special protection?