What to tell children about their father's abusive behavior.

My husband has been both verbally and physically abusive to me for over 20 years.  As far as I know, my children are not aware of this.  The physical abuse always occurred when they were not present or behind closed doors.  I have two children in college and two in high school.  I have made the decision to leave my husband, but am wondering what to tell the children.  I am debating on whether to tell them what their father has done.  Part of me thinks that it might help them in the future in their own lives.  The other part does not want to ruin their relationship with their father.  Other than being too controlling, he has not shown them any abusive tendencies.  

[kberaun41]

If you do decide to tell you children, do  this first... next time he physically abuses you.. call the police and file a report. you wont have to leave then.. but it iwll be on file. then your children will believe you later... I dealt with this...  just dial 911 and after minute hang up.. they will come anyway.. and you can tell  them you  are ok now but want a report taken.. they will do this..that is if you are ok..
If you decide not to tell them, that is fine too.. just tell them you guys just couldnt get along. they had to have heard the verbal abuse..
what i think though is next time he is abusive.. take the kids and go to a shelter and be done with the slug