Put the sensor down first

[Fugi the Great]

So you found yourself next to Yang, but you need to expand toward him because that is the only way to expand. Before you "build" that city, put up a Sensor first, then build that city on top of the Sensor. That extra 25% defense bonus will help you later. Best of all, he can't destroy the sensor unless he destroys the city. This probably will also help units defending citys against mindworms, and locusts. Morgan taught me that little trick. I just couldn't figure out why I kept getting my butt kicked everytime I tried attacking his city and why he kept getting sensor defense bonuses since I blew all of them up around the city, until I looked inside and saw a sensor. It's just a shame you can't terraform inside a city after it is already built.

[Velociryx]

Sounds like a pretty good plan in general! It's hard to knock an additonal 25% bonus for what? Two-three turns of former activity? Seems like a good value to me! :-)
-Vel.