Many dogs will keep going and going, whether they are tired or not. Some things to watch for are excessive panting, heavy breathing, wobbliness, moving slower. Unless you are doing hours of walking though you probably are not going to tire your dog out on a walk.
If you are walking on pavement/sidewalks though you will want to watch out for sore pads and make sure not to walk during the middle of the day when the pavement can be hot. We often won't notice it, but dogs are walking barefoot and are closer. I usually will put my hand on the pavement to see if it is hot or not. If the dogs pads are getting raw/sore you can put something on them like mushers secret to help and keep walks short until the pads harden up.
Dog's most certainly don't walk forever!! Some do have a maximum amount of stamina, though. Just because your dog doesn't splatter on the sidewalk in fatigue, doesn't mean it isn't exhusted!
The signs of a tired dog are well-stated by "melgrj7". To add on to what they said about sore pads--if the concrete is hot, but you need to continue walking, have your dog walk along the grass or dirt until you get home.
Once this last summer I walked my son to a play date about 3 blocks from our house. I took all the kids and dogs and we stopped by the park on the way home. At the end of our street there is a low spot where water always gathers and there was a nice sized puddle there where the curb and street meets. Alex decided she had had enough and just plopped down in the puddle and refused to move for at least 5 minutes. It took everything I had to finally convince her to get up and walk the block back to our house.
Jack is the only one of my dogs that will let me know when he's had too much but he's almost 14 so he has an excuse. it's usually bout half a mile before he starts lagging behind and then I know he's pooped. I ave yet to learn what kind of walk is long enough for Kechara and Hawk
Few years ago I decided to visit my grandmother by riding my bike. She lived about 11 miles on the other side of the city. Having one 2 year old male at the time, I realized he only went out to the bathroom that day. I knew his energy was rolling over its self so I convinced myself to bring him with me. He'd get some great exercise from running along side of me.
This dog's endurance is unreal. He didn't let the end of the leash relax going up or down a hill. Good thing where I live there is a lot of grass/dirt roads because his pads would of been sore on pavement.
Depending on the age of the dog, you want to limit how long a walk is, especially if you have only sidewalks to walk on. Sidewalks are very stressing to the joints, and can cause splaying in the knee joints if they are walked, or run too much on that hard unforgiving surface.
Certainly let her romp as much as she wants in a park, or other grassy field type areas, but until her joints close, cement should be carefully monitered.
If she as an adult, still moniter how much she is on cement, or pavement, especially when it is really hot, or really cold, but you can walk her longer on those surfaces without too much concern. I let my dogs walk on any grassey areas we encounter on a walk.
For a small dog, a couple of miles a day, spread out, is a good amount to keep her fit and happy. Interactive play, and training time, can further wear her out every day.
My small 4 pound dog will just quit walking. We'll be walking along fine, then all of a sudden the leash gets heavy, and I look down and I'm basically dragging her along because she has just laid down in the middle of the road! Thank goodness she only weighs 4 pounds so I can just pick her up and cary her the rest of the way!!
My Donatello is 18lbs, and I have the same dilemma... I'm trying to wear him out... I'm trying to get him pooped; We live in an apartment and being he's a Manchester/Jack Russel Terrier mix he has some energy he needs to burn!
We can play for a couple hours at the Dog Park, then walk another mile, and he still won't show any signs of being tired... Until we get in the truck, then he literately plops down and goes to sleep on the way home. While we're walking he won't even break a sweat or stop for a rest... Like others have said, many dogs will keep on walking despite being tired.
My suggestion is: Walk your dog in small increments... Maybe a mile the first day, add on an extra half mile or an extra mile the next time. If your dog starts getting sluggish, or starts slowing down, then maybe you're pushing it and should stop...
Like a lot of people have said, most dogs will keep going long after they're tired. With my dogs I can just tell. I have a basset that suddenly will no longer be pulling on the leash. When I stop, he'll stop and he'll start moving again a beat after I do. You can tell he's tired.
When spring finally comes, I will start riding my horse every day. We start out slowly but it is not long before we are going out for a couple of hours at a time. Susie travels twice as far as the horse, running ahead and coming back, chasing squirrels, etc. I would really like to know how far she travels. I can use the GPS and tell how far I have ridden but I am sure I would have to at least double the distance for Susie. I have taken her on some Rides where we leave at 8 am, have a lunch break, and get home at four or five in the evening and she is going the whole time, plus swimming in every water hole we come to.