A heartbroken dog owner who decided to put down her "ticking time bomb" St Bernard is urging other buyers to be vigilant.

Sharon Herrington, from Peacehaven, said she had to act over fears Bear - who weighed more than 60kg - would launch a fatal attack.

The dog had already bitten two strangers and she was worried about the safety of her family.

Sharon, 53, and husband Cyril Herrington, 65, got Bear when he was one, after his previous owners gave him up due to ill health.

They say he wasn't showing signs of aggression then but, within six weeks, had started lunging at people.

The couple - who are experienced dog owners and have had two St Bernards previously - spent more than a year trying to “fix” Bear.

But they decided he couldn't be saved and the best thing to do was to put him down.

Sharon thinks bad breeding is behind the aggressive behaviour - and is warning others to check the bloodlines before they buy.

She said: "He was like a ticking time bomb - we were scared he would launch a full-blown attack on someone.

"I couldn't trust him enough to have the grandchildren in the house.

"It's horrendous without him. We're heartbroken to have had to do this, but it felt like the only responsible thing to do.

"There’s a huge hole in our lives without our massive bounding dog.

"But we'll only be able to eradicate genetic aggression if people who can trace back a bad bloodline do the same.

"They need to do routine checks on breeders more frequently and take away licences if things like this are happening.

"Anyone can apply for a licence but they should be checked more thoroughly - there should be more regulations.

"Plus we have far too many dogs in the UK. We should concentrate on all those dogs needing a home rather than breeding more."

The couple, who have four children, chose the breed because they are usually docile, they said.

Sharon looked for support online after Bear changed, and when anti-aggression training did not work.

She learned from a group called St Bernards With Issues that the aggression was likely to be genetic.

Sharon said: "My kids could climb all over the St Bernards we’ve had before.

"They're a gentle, loving, breed, and that's why people buy them.

"You could definitely tell that it was genetic and not behavioural [with Bear], because nothing made it better.

"It was very isolating - we couldn't have anyone over and nobody could go near him if we were out.

“It wasn't his fault. I think he came from a bad line. We tried our best but it wasn't safe.

"He was ten and a half stone - like a Shetland pony.

"I don't believe in putting animals down unless there's something really, really wrong, but we did everything we could to help him.”

Sharon says Bear went for their eldest son when he visited their home about four weeks after they took him into their care.

He later stood on his hind legs and snapped at Cyril who was trying to diffuse a scrap between Bear and another dog.

But the couple knew that drastic action was necessary when Bear bit the arm of a neighbour's guest in March.

He then ran at the plumber and bit him on the backside on March 15.

And they made the extremely difficult decision to have their pet put to sleep on March 29.

She said: “This was heartbreaking for us, but if it’s in their DNA there’s nothing you can do.

"I'm a very big animal lover, and I put animals first, I’m so upset that Bear and all these other dogs are being put to sleep.

"If anyone moved in a way that he hadn't predicted he go for them, and if someone walked behind us he'd go rigid.

“Bear had fear aggression - that’s genetic. It means they have a fight response to everyday situations that they can't control."

Sharon and Cyril now have a new rescue St Bernard, Rosie, aged six, who they got from the St Bernard Trust.

Sharon said: "There are some great breeders out there, but also a lot who only care about the pound signs.

“Ask to see the mum and the dad with the pups - if they don’t let you do that it's a definite warning sign.

“Look at the environment they are living in. Some of these puppy farms just have a stable block type thing.

“Look at how clean the conditions the pups are being kept in, and how the people interact with them.

“Check whether the pups have outside time and exposure to people and places."