NEW YORK – Kelly Lucas blissfully wed three years ago. For her cats, it was more like hell.

Happy to have married a fellow cat person, Lucas and her husband were hopeful they could blend their pets: two males for her and a plump old moody female for him. It was a no-go, then and now.

“I wouldn’t call them oil and water,” Lucas said. “It’s more like gasoline and fire. BOOM! It’s been over three years, and they still hate each other with a passion.”

The Atlanta couple, who also have an 18-month-old human baby, keep their animal camps apart using a Plexiglas-reinforced screen door on the stairs of their two-story house. It’s a measure they had hoped would be temporary.

“Basically all it serves as now is a buffer so they can hiss and swipe at each other,” Lucas said.

Merging pets when moving in together usually has a happy ending, but it can take time, patience, medication (for the pet) or the help of an animal trainer or behaviorist, said Dr. Chessie Green, who heads the N.C. Veterinary Medical Association in Raleigh.

“It goes pretty well for probably eight out of 10 of my clients who blend their families,” she said. “Most people don’t consider their pets before moving in. Sometimes people are forced to find them new homes because they don’t get along or somebody is allergic.”

Suzanne Finch in San Diego didn’t have allergy issues, but she’s had her share of cat-astrophes.

The fur flew in 1990, when she realized just how much her boyfriend’s cat hated her three cats – and Finch herself for that matter – after the whole gang moved in together.

“My boyfriend’s cat loved him and was a jealous mistress. One of mine was a queen bee,” Finch said. “His would pee on the carpet, and my Queenie would poop on the carpet. We finally had to put plastic drop cloths all over the floor for the entire time we were together.”

That turned out to be four long years, until he and his cat moved to Detroit and she stayed in California.

Making it work involves many variables. But Valarie Tynes, a veterinarian and behaviorist in Sweetwater, Texas, has one key observation.

“The first thing pet owners should be aware of is the importance that early socialization plays in future behavior of a dog or cat,” she said. “A cat or a dog that has not spent much, if any, time around other dogs and-or cats during their adolescence will be much less likely to ever get along well with other animals.”

Getting two adult cats to live in peace can take longer and pose greater challenges than blending unrelated dogs, Tynes said.

When combining dogs, Green suggests introducing them on neutral territory first, using leashes. “Do it in a neighbor’s yard or the park or a friend’s house, where the dogs don’t have a stake.”

Don’t convey your own anxiety by holding the leashes too tight.

“Dogs can read that,” Green said. “Everybody in the environment needs to stay calm.”

Let them sniff each other and investigate, and pay attention to their body language. Are their ears down or back, indicating anxiety, fear or aggression? Are their tails up or down? Down might mean they’re feeling anxious or scared; up signals confidence. A tail straight out can mean either neutral feelings or aggression, Green said.