This shar-pei sits in his stylish, cylindrical metal crate by Bowhaus. Whether it’s pricey or a bargain, the crate must remain a dog’s safe retreat.

MCT / CAROLINE CHEN

Twenty years ago, even experienced dog owners did not use crates. Today, they are a must-have, especially for puppy training.

While they may be ubiquitous, crates are not always used properly. Here are some of the most common mistakes people make with these important tools:

Size matters

Crates are not playpens; they are simulated dog dens. The ideal crate allows a dog to stand up, turn around and lie down — and not much more. Crates that are too roomy encourage dogs, especially puppies, to eliminate in a far corner.

Rather than buying a succession of crates to accommodate a growing puppy, get the size that your dog will need as an adult. If it’s a wire crate, buy an inexpensive divider panel that will allow you to reduce the size. If it’s a plastic kennel, use a heavy-duty cardboard box to displace the extra space in the crate. As your puppy grows, replace with a smaller box, until he has reached his full size.

Tip: Don’t buy fancy dog beds unless you know your dog is not a chewer or a stuffing eater. An inexpensive choice for a crate bottom is a bathroom rug — the skidproof backing will keep it flat and unbunched.

Time for a break

The general rule of thumb is that dogs should not be crated for more than four hours at a time. To keep your dog occupied in the crate, buy a Kong (a tough plastic toy sold at most pet stores), stuff it with cheese or peanut butter, then freeze it so it lasts even longer.

Tip: Don’t forget to subtract the food and treats you give to your dog in the Kong from his overall calories for the day.

As Quasimodo said . . . “Sanctuary!”

Your dog’s crate is supposed to be the one place where he can retreat. It is his ultimate “safe place.” Children need to be taught that a dog’s crate is absolutely off limits. They should never follow a dog there, or attempt to get inside the crate.

Tip: This applies to cats and their carriers, as well.

You talking to me?

Dogs unaccustomed to the crate or frustrated that they cannot get out usually resort to barking. Cardinal rule: Never let a barking dog out of a crate. If you do, you teach the powerful lesson that complaining is what gains his egress. Instead, wait for a pause in the barking — no matter how brief — before unlatching the crate door.

Tip: Lots of short intervals in the crate, rather than just one long session, will help your dog get accustomed to it without stressing him out to the point where he barks and protests.

Dinner is served

The quickest and most powerful way to get a dog to love a crate is to serve dinner in it. Similarly, you can hide high-value treats and rewards inside the crate, so when the dog meanders by and goes in to investigate, he is rewarded with a biscuit or a rawhide chew.

Tip: A surefire way to get a dog to love going to his crate is to give him a treat each and every time you put him in. Once he goes there willingly, add a command, such as “Go crate!” or “Kennel up!”