If your dog is experiencing constipation on a regular basis you should add roughage to his diet such as canned pumpkin (not pie filling kind). A spoon full on the dog's food should keep his bowels hydrated and his feces soft enough to pass.
A spoon of mineral oil on his food can also be used but should not be used all the time.
In addition, if there is a possibility that your dog may have ate a non food item, then your dog needs to see a Vet to rule out an intestinal blockage which can be life threatening if not treated.
If your dog is experiencing other symptoms such as vomiting, not eating or drinking or you notice any of the signs listed below, the the dog also needs to see a vet.
If your puppy becomes dehydrated. You can tell by pulling up the skin between his shoulder blades and seeing if it flows back down normally. If it stays tented or is slow to return to normal, your dog is dehydrated and needs fluids immediately and should see a vet as soon as possible.
If gums and tongue become pale and not a normal pink color.
If rectal temperature is over 103F (101-102F is normal)
If your pup becomes lethargic and non responsive.
We can't always be prepared when our pets have problems, but it is up to us to get them the care they need.
Here is a few places that may help if your dog needs vet care.
This group helps low income families with vet care.
This organization help people with emergency medical care in some cases.
Care Credit http://www.carecredit.com
Quick application and approval for care credit card. You can sometimes apply and get approval while you are at the vet office.
Hope this helps.