Vector 3 do/while problem

I could barf all of my code here but, if your like me, you might skip over this question.

I have a randomly generating map script that creates a line of cubes and at the end of the line creates a city.
the city then makes another line, and that line makes a city, and that city makes a line, etc.

The script uses a for loop that creates a random amount of cubes. an empty Vector3 "cloneposition" is incremented by another Vector3 "direction".. the for loop then places a block (or a city) at cloneposition

direction is defined like this

 do{
           direction = Vector3(Random.Range(-1,2),0,(-1,2);
 while(direction != Vector3(0,0,0); // I do this so that the line moves at least once in some diagonal or straight line

THE PROBLEM : I don't want the lines retrace themselves, if a city can a line that moves in the direction that overlaps the old line. I do not want this to happen. I decided to add a static variable "olddirection", that would be set to the negative of direction's x and z parameters every time the direction is decided upon, and then add a line that makes sure that the direction is not the same as the negated last direction.

It looks a little like this :

 do{
     direction = Vector3(Random.Range(-1,2),0,Random.Range(-1,2));
 }while(direction == Vector3(0,0,0) && direction == olddirection);
 olddirection  = Vector3(direction.x * -1, 0, direction.z * -1);

It doesn't work! something must be going wrong. The boxes that are used in the line have colliders, so it is essential that they do not collide with each other (except if the lines cross at one point, that is supposed to happen). I just don't know what to do. Thank You for reading this. I would have skipped over it

Here is the rest of my code incase i did something else stupid

 var thisobject : GameObject; //this object, ahh come on
 var direction : Vector3;//this rows direction
 var emptygameobjectprefab : GameObject; // the roads, these can change to building    
 var length : int;//number of segment
 var cloneposition : Vector3; // this is moved to judge to position of the next piece
 var city : GameObject; // the city prefab
 static var numoftowns : int; // number of towns on the map
 static var maxtowns = 50; // the requested number of towns
 static var olddirection : Vector3; // the direction one round before it
 do{
     direction = Vector3(Random.Range(-1,2),0,Random.Range(-1,2));
 }while(direction == Vector3(0,0,0) && direction == olddirection);
 olddirection  = Vector3(direction.x * -1, 0, direction.z * -1);
 cloneposition = thisobject.transform.position + direction;
 
 length = Random.Range(4,51);
 if(numoftowns <= maxtowns){
     for (var i = 0;i<length;i++){
             Instantiate (emptygameobjectprefab, (cloneposition + Vector3(direction.x /2,direction.y,direction.z / 2)), Quaternion.identity);
             cloneposition += direction;
     }
     Instantiate (city, (cloneposition-(direction / 2)), Quaternion.identity);
     numoftowns++;
 }

Thanks a bundle, have a Quishtay™ day