Controlling automated workers

Is there any way to prevent automated workers in Civ IV from replacing previous improvements (as there is for Civ III)? For instance, how do I prevent automated workers replacing my lucrative towns with wimpy workshops or farms?

 

I think the answear is in the options menu

 

Got it! Thanks!

 

Yeah you got to love the workers theory of bulldozing Cleavland so they can plant beans.

 

Something else, when i like click on a unit, the game quickly goes to another unit that isn't doing anything (for instance I move a worker, he's out of movement, but I still want to order him to built something).
I have to ask this after having a rather anoying thing : i moved my great enigineer and wanted him to move a little more, the game moves me to another unit and in my confusion I hit the 'hurry production" and finish a lowsy barrack !