It just seems really wierd that he would try multiple times to kill Gaara with lower level ninjas.
If he really wanted Gaara dead because Gaara was too dangerous, why didn't he just kill Gaara himself? He should be powerful enough, he is a kage, and it was shown that Gai (a jounin) was able to handle Gaara's sand without a problem in the Chunnin exam.

Now, the sand is using Gaara as a weapon, I thought they were scared of him and tried to kill him.

Maybe its all a ruse. Maybe Kazekage didn't really try to kill Gaara, more than try to measure Gaara's abilities and make him more dangerous.