Change them regularly
It's important to change your logo regularly, so that people get confused.
Many years ago I worked for a large insurance company who succumbed to the dreaded marketing agency hype and decided to have a new logo. Much money was spent and the entire staff (several thousand) was bussed down to London from all around the country, in the middle of winter snowstorms, so that they could attend the official launch, complete with TV personality.
Three months later they scrapped it and tried a different logo!
Three months after that they scrapped THAT and tried yet another.
Guess what? A few months later they had another change of mind and went to yet another one - strangely similar to the original one. The 'Year of the Four Logos' lived on in company memory.
Champers all round for all the major London marketing drones!