Right-hander Aaron Cook, the veteran of the Rockies' homegrown rotation, has been offered a three- year contract extension in a move to try to keep the nucleus of the team together long term. The Rockies already exercised their $4.5 million option on Cook for 2008. But he could be a free agent after the season, and the Rockies are hoping three years of additional security will entice him to make a commitment. The Rockies are offering a $30 million guarantee with an option year, a source told the Rocky. Cook has indicated a desire to remain with the Rockies, and while he would be giving up some money in exchange for the contract security, he also would be 32 when the extension expired and would have another opportunity to test free agency if he wanted.