Crushed eggshell should work just fine. Do you ever give them raw chicken/turkey necks? They are an excellent source of calcium for dogs.
Proud Owner of:
Charlie- 6 year old Border collie cross
Alvin- 2 month old Toy Pom
Roxy- 4 year old Sheltie/Pom
Angel- 12 year old Persian (deseased Dec 6, 2008)
An animal's eyes have the power to speak a great language." ~ Martin Buber