The fights often involved maiming and/or killing animals and fighting roosters had metal spikes jabbed into their feet to help them kill each other, RSPCA officers said.

They identified Ballan, Maryborough and Avoca as hot spots for fights and said they were big business.

RSPCA chief inspector Kevin Apostolides said serious organisers and their clients travelled around the country to attend fights, which often had minimum bets in the tens of thousands.

A fighting dog could sell for up to $30,000 and a rooster could fetch up to $5000.

Mr Apostolides said dog and cock fighting, while illegal, was difficult to stop because of its organised nature and small penalties.

Fights were held in secret locations at short notice with an invitation-only attendance list.

People invited to the fights were told how to dress and given secret passwords to get in while a network of lookouts, called "cockatoos", watched all roads leading to the fights and gave warning if an unauthorised vehicle approached.

"The people who are doing it are usually career criminals and the evidence is often circumstantial at best," he said.

"We have gone into places where we know most of the leaders in dog fighting are present and they say `we are having a private dog show'.

"It's incredibly difficult to prove under the Act as you have to catch them doing it.

"I can tell you name of a guy doing it, I can probably even tell you the names of his dogs, but I can't prove he's a dog fighter."

Acting Ballarat police Superintendent Vic Dunn said dog fighting was difficult to monitor.

"They are often held in remote areas, so any attempts at surveillance are rapidly detected," he said.

Acting Supt Dunn said police were presently investigating a fight that had been held at Avoca.

He was aware of about "four or five" dog fights held in the region in recent years.

Mr Apostolides said fight organisers faced a maximum penalty or 12 months' jail or $25,000 - recently increased from $12,000.

But with fights turning over hundreds of thousands of dollars, dogs worth tens of thousands and roosters worth thousands, the penalties were too small to threaten serious fight organisers.

Mr Apostolides said dog and cock fighting was dangerous to investigate, because organisers and people attending the fights were often hard-core criminals.

"One of the great problems the RSPCA has is we don't have the resources or staff to put into it properly," he said.

Mr Apostolides said he lacked the resources, and his staff lacked the training, to investigate dog and cock fighting safely.

Only 18 months ago a man was shot dead at a cock fight at Rockbank, he said.

"They're the sort of guys we're dealing with," he said.

"They're not the sort of people who stick their hands up and say "yes sir, you've got me".

"I've had enough of my officers injured doing what they do to expose them to that level of violence."