Almost as soon as he arrived, K9 Mark IV left Sarah Jane to stabilise a dangerous black hole in space which had been created in Switzerland. He could only speak with Sarah Jane occasionally via a cabinet with a space-time link when the orbit of the black hole intersected with Earth's and did not know when he would complete the job. (TV: Invasion of the Bane) However, he returned to Earth very briefly during emergencies. He did so on two later occasions in order to render vital assistance. The first time, he fought Mr Smith in pitched battle to give Sarah Jane time to upload the Armageddon Virus. (TV: The Lost Boy) The second time, he quickly uploaded TARDIS base codes to Mr Smith, assisting the Tenth Doctor in returning Earth to its correct location in space. (TV: Journey's End)
In early 2007, K9 was reactivated by the Tenth Doctor; Sarah Jane was unable to go to any humans for repairs prior as the parts inside K9 could change history. K9's repairs were short lived. In battling Lucas Finch and his Krillitane invasion at the school the next day, Mark III blew up a vat of Krillitane oil, which was now lethal to the Krillitanes destroying himself and the Krillitanes in the process. (TV: School Reunion)

As a Former Law Enforcement Officer, I formed Dallas K-9 with integrity. I'm the Assistant Director over the South Region for Protection Sports Association (PSA). I'm also a National level Certified Decoy for Protection Sports Association (PSA). Here at Dallas K-9 we strive to produce The Belgian Malinois, Dutch Shepherd, and German Shepherd with Solid Nerve, Extreme Drives, Clear Heads, Full crushing Grips, and strong Hunt drives with powerful noses. These qualities are needed in order to perform the job that he/she is given. Our dogs are raised around kids and are very well socialized. Our puppies are properly imprinted before being placed in their new homes to make sure it's a good fit for both the puppy and family.
K9 Mark 2 had some obvious commonalities with the Mark I that had preceded him. However, as he had almost completely lost his personal memories, he was forced to reacquaint himself with the world around him. Toward this end, he downloaded thousands of human movies onto his memdrive, which peppered his speech with 20th and 21st century English colloquialisms that his "brothers" did not typically employ. (TV: Alien Avatar) Despite his negative opinions of emotions, (TV: Mutant Copper) he asked questions about some, such as fear (TV: Fear Itself) and love (TV: Aeolian). He even showed some, laughing when he saved the day, feeling fear (TV: Fear Itself) and being angry. (TV: Regeneration)
A K9 officer and his or her dog, should undergo lessons in maintaining the police dog normative once a week. A K9 handler and a police dog improve their work per Shutzhund dog training, tracking training, bomb detection, and K9 tactics. We simulate different situations that may pop up during serious police work, using automobiles, a garage, sport , elementary schools, shopping centers, etc.
K9 helped Sarah Jane to defeat Moreton Harwood's murderous Hecate Cult. (TV: A Girl's Best Friend) Circa 1983, K9 Mark III and Sarah Jane lived in semi-detached house where their gate bore a "beware of dog" sign and Sarah Jane permitted him outside unconcealed. Sensing danger, he advised Sarah Jane to either not go out, or to take him with her. She declined, and K9 thus did not accompany her to Gallifrey. (TV: The Five Doctors) K9 accompanied Sarah to an archaeological dig in Egypt. (COMIC: City of Devils) In the early 1990s, K9 assisted Sarah in investigating a supposedly haunted house. (PROSE: Housewarming)
In early 2007, K9 was reactivated by the Tenth Doctor; Sarah Jane was unable to go to any humans for repairs prior as the parts inside K9 could change history. K9's repairs were short lived. In battling Lucas Finch and his Krillitane invasion at the school the next day, Mark III blew up a vat of Krillitane oil, which was now lethal to the Krillitanes destroying himself and the Krillitanes in the process. (TV: School Reunion)
After K9 Mark I regenerated into K9 Mark 2, his design was radically altered. His ear probes were replaced with larger silver aerials. A set of blue lights on his head flashed when he spoke. Most of his body was dark silver and a silver dog bone was located under his neck. He seemed to have the same capabilities as Mark I but was presumably more advanced. (TV: Regeneration)
K9 Mark 2 was the result of the activation of the Mark I's onboard regeneration unit. He had only very limited memories of his past as the Mark I. He had many adventures with Alistair Gryffen, Jorjie Turner, Darius Pike and his new master Starkey. (TV: Regeneration, The Bounty Hunter) Orthrus was an attempt by Drake and the Department to replicate K9, but it was of vastly inferior design. (TV: Jaws of Orthrus)
The handler and dog must also be able to pass the police test, which involves controlling the dog fully, even after giving the dog the attack command. The dog must stop immediately and fulfill any command it is given by the handler. There are specifications of training involved in using trained K9 police dogs in the airport, marine ports, railroads, in a metro station.

This K9 exhibited the ability to sense and warn others of danger. He was also more mobile than his predecessor, despite his problems with the swamps of Delta III, able to lift himself up on small support rods so that he could climb stairs (PROSE: The Shadow of Weng-Chiang, TV: The Power of Kroll, The Armageddon Factor) The Doctor often used a glib remark to disarm those who were surprised by K9's appearance, such as "They're all the rage in Trenton, New Jersey." (TV: The Stones of Blood)

A short story, "Moving On", in Virgin Publishing's Decalog 3: Consequences anthology and the Big Finish Productions-produced Sarah Jane Smith audio play Mirror, Signal, Manoeuvre (both written by Peter Anghelides) indicate that K9 Mark III broke down and Sarah was unable to repair it as the replacement circuits would not be invented for several centuries.
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