I've done that, and it works well. This is something that should only be considered with larger breeds such as the kuvasz, maremma sheepdogs, and great pyrenees, and any similar sized or larger breeds. Home enemas should never be attempted on a dog smaller than 70 lbs, as it is easy to get the dosage wrong and overfill the colon in smaller breeds, which can cause all sorts of problems as well as perforation.
Large, XL, and giant breeds, tolerate enemas well, and provided you use common sense (never use otc phosphate enemas), it is perfectly safe on these dogs.
Glycerin and Water Enema
Glycerine works for constipation in my dog.
My 105lb (intact) kuvasz bitch has problems once or twice a month during the summer. I get a 2qt enema bag, add 6-8oz of liquid glycerin and fill with warm water. Insert the hose a bit, and let it flow for a minute then slowly push the hose deeper. The further in you can get it with gentle pressure, the better. Works ever time, usually before she can finish the bag.