Gordon Wyeth of West Dean, near Chichester hopes the camelid pair will help protect 500 ewes due to lamb at the farm in April.
The sheep that died in the attack last year appeared to have been herded by dogs into a tight group against a fence and gate where they panicked and either died from shock or were crushed in the flock, police said.
Many of the dead animals were pregnant and the incident was described as the worst attack of its kind in living memory.
Now professional shepherd Lizzie Rough has introduced alpacas Tom and Jerry into the 50-acre field at the same site to see off any threats while staff are away.
Mr Wyeth said: “The reason why we have these alpacas now is because of what happened here a year ago.
“We want to avoid dog attacks on sheep at all costs.
“We have scanned ewes from this flock to check their pregnancy and we estimate that we have already lost more than £4,000 in lost lambs.
“We believe these losses are largely down to dogs worrying our sheep.”
Alpacas are docile creatures, but are sometimes bought to protect birds and other livestock, as foxes and other predators are wary of being trampled.
Lizzie Rough, who bought the alpacas from a Devon sheep farmer on Facebook, said: “We often find dogs bounding up among the sheep and the owner some distance behind.
“We can’t be here all the time looking after the sheep, so now we have Tom and Jerry to guard them.
“These alpacas are fairly shy of people but they are alert to predators.
“If a dog is on a lead, then they’re unlikely to approach but they may well chase loose dogs that they see as a threat to the flock.”
A popular footpath runs through the field, linking The Trundle with The Centurion Way, and signs have been put up to warn dog walkers to keep dogs on leads when walking through the field.
A fundraising page saw well-wishers rally to help the farm in the aftermath of the attack, which cost Mr Wyeth an estimated £17,000.
Ms Rough said: “Even if a dog is not biting sheep it may be scaring them by running among them when they’re pregnant and then they can lose their lambs.
“The lambing results for this particular flock are expected to be poor.
“It’s not simply an animal welfare issue - dog attacks hit farmers’ livelihoods.
“Ultimately this affects my job and jobs for other young people in sheep farming.”
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