Have you tried looking under/inside the chair. I'm willing to bet that there is some way of locking the chair to keep in from rocking.

Call the manufacturer if you can't find the mechanism.

I googled the title of your post and got some hits that might at least give you a few clues. Most involved jamming the mechanism one way or another, One site thot there might be a conversion kit depends on the manufacturer. Here's one but there were 4=5 others.

Here is a link that might be useful: Rock

Not exactly what you asked, but.....

If your situation is chronic, I would strongly recommend you consider an "electric chair"....one of those recliners with an electric mechanism built-in that raises or lowers the occupant. They are capable of raising the occupant to a 1/2-standing position allowing much easier access to a compromised person. From experience with my aged/demented mother, I came to regard them as nearly indispensable.

Link to examples provided. I have no association with any vendor other than as retail customer.

Here is a link that might be useful: pictures of lift-chairs

I have an electric reclining chair if I push the button it will raise my feet or lower the back for reclining. I sometimes I find it hard to get out of it. I have found that if I don't lower it all the way it is easier for me to get out of it and it doesn't rock.
Mary

Thanks so much for your thoughts. Jamie is 18 and we thought about a lift chair, but we are trying to keep as much muscle tone as we can. We notice that even little changes in excercise can effect him.

We love our lazy both rocker/recliner. We are having difficulty getting out of the chair