Walking my dog

Question
I have a 7.5 lb. toy poodle (spayed female) almost 4 yrs. old.  We enjoy going for long walks.  So far, she's gone 3 miles and ran in circles in the house when we got home.  Can I keep building the distance safely?  What would be a safe maximum distance to work toward?  Also, I just added a 4 lb. male toy poodle 1.5 yrs old (not to the household.  I can always carry him if he gets tired before my girl does, but am also curious how far he could safely walk.  If a dog wants to keep going, can it generally be considered safe to let them?

Answer
It's not always safe.  Dogs can be very stoic in an effort to please you.  If the weather is good, and the dogs do not get tired or dehydrated (pinch up a fold of skin - it should go back down quickly, or press your finger against the dog's gums, which should be pink - sticky gums are an indication of dehydration), it's probably ok for an adult dog.  Keep an eye on the dogs' pads, too.  If they are getting cracked, or dry, you may be doing too much, especially on pavement.