Shield of Sand

Whenever Gaara is about to come to harm, a shield of sand will automatically surround and protect him. The sand will react regardless of Gaara's will, even protecting him from self-inflicted injuries. This was first believed to be enacted by the One-Tailed Shukaku's desire to survive, although it was later revealed that Gaara's mother, Karura, had her love and will seeped into it. The shield is capable of withstanding considerably strong attacks and projectiles, and can be hardened to a point where it's stronger than even Raikage's strength and the Gold Dust. Gaara can also completely surround himself in the shield to further increase his defensive capabilities. The shield is so fast that even Sasuke's Amaterasu failed to breach it, earning the name.

In Part I, the shield's power was considerable in speed and strength. However, it could have been easily defeated with extreme speeds and brute force, such as Sasuke's Chidori and Rock Lee's Reverse Lotus.

In Part II, however, the shield showed a great increase in speed, to the point where it could guard against Amaterasu and defend against the Fourth Kazekage's Gold Dust.

Trivia

 * Despite that Shukaku is the source of this technique, this and other techniques remain with Gaara even after having it extracted from him. However the Fourth Kazekage stated that Garaa's mother is in fact the source of this technique, which explains why it's still active even after Shukaku's extraction.