I don't know if your dogs are already on a heartworm preventative, but there are heartworm preventatives out there that treat hookworms, roundworms and tapeworms too.
Like Iverhart Max for example and it's not very expensive either. On drsfostersmith.com (with a prescription from your vet) a year's supply for dogs between 50 and 100 lbs is $ 56.28.
And I think the shipping might be free: http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=16602
But anyway, that way you don't have to buy different kinds of preventatives for each type of worm. You just give your dog 1 pill each month and that's it.
Like Iverhart Max for example and it's not very expensive either. On drsfostersmith.com (with a prescription from your vet) a year's supply for dogs between 50 and 100 lbs is $ 56.28.
And I think the shipping might be free: http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=16602
But anyway, that way you don't have to buy different kinds of preventatives for each type of worm. You just give your dog 1 pill each month and that's it.