What would you recommend to prevent/cure chronic constipation?
Kefir! See if you can find someone in your area with a kefir bug and use it daily.
It's really important to get on top of this issue, as it is a risk factor for bowel cancer.
If you have done all the usual things - like increasing fibre, ensuring adequate water, regular exercise and so on, then the best advice I can give you is to have a consultation with a naturopath or clinical nutritionist.
All the best