Psychics are a species with the ability to see future. Along with these abilities, they have side abilities gained from their power of premonition. Some psychics are hard to kill seeing as how they know incoming attacks and what is going to happen to them.
They are also hard to kill because any species can be a psychic like humans, witches, practitioners, etc. and some of these beings have other powers that they can use hand-in-hand with their psychic ability by seeing what's going to happen and prevent it.
Psychics have different mode of operations. Some use their abilitiy to help prevent bad things from happening. Some use their ability to their own advantage like winning the lottery. Some use their ability to protect themselves by protecting themselves from incoming attacks they see coming.
There is a pyschic spell rarely used most likely because not many people know about it and/or know the spell. The psychic spell defends the caster, making them immune to all of a psychic's abilities including premonitions, intuition, and the rest. Psychics will not be able to get a premonition or any intuition from that person by touching them. They cannot recieve any premonition involving the spellcaster and feel their intentions or whether they're good or evil.
However, the spell may not take its full effect if someone close to spell caster did not cast the spell. There is a loop hole left open if that is closed. The psychic can pyshically contact that loop hole and they may get a premonition of the spellcaster through them, especially if the loop hole and the spell caster are in a close relationship or are involved in a situation. This will ruin the caster's plan to avoid the psychic's great knowing and plan to stop the psychic from knowing his/her plan. Also, the spell doesn't last forever.
This was displayed when Marcus and Heather cast the psychic spell inThe Eclipse. Meredith could not sense anythign from them. However, the loop hole, their son, Elijah did not case the spell. She could sense evil from him through his family's evil blood and would get some premonition involving his parents through him.
This was displayed a second time when Chris told Alec he feared that Meredith would find out he was a Surgo through her premonition power inThe Reincarnation. Cristina said she knew a witch who knew the psychic spell. She gave her witch friend's location to Alec and Chris. They went to the psychic-witch, Phoebe and she performed the spell when Alec gave her the location of the Bonum Headquarters, something she found more valuable than money which the first offered, especially since the Bonum Book lied there. They tested it when Phoebe tried to get a premonition from Chris but couldn't. Phoebe said that they would have to come to her when the spell wore off which happens in some weeks.