Some dog parks post rules on fence posts or websites, but often rules and issues of dog park etiquette are unwritten and unspoken. And failure to obey them can result in dogfights, bites or conditions that are just plain unpleasant for dogs and people.

Dog parks are not for every dog, but some owners are slow to recognize that. The least popular dog in any park is the dog that behaves aggressively toward others. Some parks have signs that say aggressive dogs must be removed immediately, but usually no official is on site to enforce the rule.

Before taking a dog to a leash-free area for the first time, see how the dog behaves around small groups of dogs in your neighborhood, said Kathy Reck, behavior coordinator at Animal Friends in Ohio Township.

If that goes well, consider a visit to a dog park on a weekday when fewer dogs are around. Weekends and weeknights after work and school are the busiest times.

If your dog is aggressively chasing or attacking other dogs, remove the dog immediately, Ms. Reck said.

Not all dogs enjoy dog parks, she said.

"If the dog is hiding under the picnic table and clinging to your side, that dog is not having fun. Some dogs would rather play with people than with other dogs. If your dog is being bullied - or is the bully - take the dog home.

"Dogs are off on their own in leash-free areas, but you should watch your dog the entire time."

Ideally, all dogs in a dog park should be well-trained and should immediately "come" when called by the owner. "But that's unrealistic in a dog park setting" when dogs may be having too much fun to obey commands, Ms. Reck said.

Don't take treats, dog food or people food into a dog park, she said, because that could prompt some dogs to fight over the food.

"Also, don't take a high-value toy into the park."

Some dogs have special toys that they really love, and they like to carry them in their mouths wherever they go. Some dogs, like some toddlers, are not good at sharing the things they love.

Be especially attentive when small dogs are running off-leash in the same area as big dogs, Ms. Reck said.

While owners often worry that their small dogs could be hurt by big dogs playing rough, many owners don't realize that some small dogs pick fights with big ones in what could be called the canine version of a Napoleonic complex.

"That's why we have small dog socials at Animal Friends," Ms. Reck said. "We sometimes see a problem when dogs of different sizes mingle."

Here are some other etiquette rules:

• Always pick up feces and place it in proper receptacles.

• Make sure your dog is up to date on inoculations. Although no one is usually at a park to check shot records, a mix of dogs is a recipe for spreading infectious diseases.

• Puppies younger than 4 months old are banned at many dog parks. Many breeders, trainers and veterinarians believe young puppies should not be taken to dog parks or events with large numbers of dogs because puppies are at high risk of contracting infectious diseases even if they are up to date on shots.

• Dogs "in heat" should never be brought to a dog park because the female dog could cause male dogs to fight.

• In warm and hot weather, make sure dogs do not become overheated. Dogs can quickly die from heat exhaustion or dehydration. Call your dog back to you for periodic breaks and make sure he drinks water. If the park does not have water, bring water for your dog.

All dogs can benefit from training classes, which are offered by Animal Friends and other shelters, as well as by professional trainers, pet stores and clubs. Attending a training class before visiting a dog park can give the owner better control over the pet and give the owner some indication of how his dog gets along with other dogs.

Owners leery of going to a large leash-free area filled with dogs and owners they don't know might consider the Dog Park Rental Program at Animal Friends. The shelter has two large fenced areas containing agility equipment. Owners can set up a play date with dogs that their dogs know and like. As many as 10 dogs at one time are allowed in the area, with a fee of $5 per dog. Advance reservations are required.

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