Forrest Taft asks the question, "What does it take to change the essence of a man?" to an oil worker. A similar question is posed and answered in an aftershave commercial by Kelly LeBrock. Steven Seagal and LeBrock were married at that time.
The final scene when Forrest Taft gives the speech about the oil companies and air pollution, was originally 11 minutes long. Audiences complained that it was overlong and preachy. The scene was re-edited before release.
After Warner offered Seagal the directorial reins for this film, then titled Rainbow Warrior, the budget blew out when bigger and more explosive action scenes were written into the screenplay. Warner turned to indie production company Largo Enetertainment to share some of the cost. In return, Largo would get the international rights to the film. However, after Under Siege opened, and performed beyond Warner's expectations, Warner decided to fully finance the film themselves.
On Deadly Ground was not Seagal's first choice to make his directorial debut. He was initially offered the mafia drama "Man of Honor" as a starring/director/writer vehicle by Twentieth Century Fox and Morgan Creek Productions, but cost overruns, and Fox's unwillingness to plonk down $30+ million dollars for the film, forced the pic to shutdown, just weeks away from filming.
When Danish stuntman and actor Sven-Ole Thorsen met Steven Seagal on the set, he was asked by Seagal to kick him to show what Sven-Ole was capable of. Sven-Ole hesitantly kicked Seagal, who caught his leg and threw him to the ground. Seagal asked Sven-Ole to kick him again, giving it his best shot. Sven-Ole kicked him as fast and hard as he could and Seagal fell to the ground. When shooting a scene together a day or two later Seagal hit Sven-Ole in the throat, resulting in Sven-Ole being knocked out for 3-4 seconds. It looked so realistic that Seagal, the director of the movie, decided that Sven-Ole's character, Otto, died, and Sven-Ole's remaining scenes were cut from the film.