My views;
I would conduct exit interviews on each employee leaving and make out a chart of reasons-better prospects,unhappy environment.clash with superior,lack of growth,personal problems etc.
This will give you an idea of why people leave.
Analyse these inputs with your ideas and discuss with other HODs.
Exit interviews if well conducted can be a good source of information,even taking into a/c exaggerations and biases of exiting employee.
Attrition is a challenge for HR,though they may not be able to control it by their actions.
HR can consider following aspects:
Is remuneration fair and equitable considering the industry and their own profitability state.
What are the perks offered? Are they in line with industry standards??
How do your supervisors and mangers deal with staff?
Personal experience suggests people run away because of their immediate bosses more than organisation.
sometimes shifting an individual to another department retains the employee.
After all attrition has its own costs-training,cost of selection etc.
Are your roles and responsibilities well defined.
Every employee/supervisor knows his place,role and job??
Is there a career ladder??
When employees leave we must try and find out who is responsible for the departure??What specific factor caused his departure??Which department has highest exit rate?
Do conduct surveys and manager sensitisation capsules.
Do walk around HR practises and meet employees on shop floor and informally also.You will understand them better.
Do not have an attitude-so what if X leaves there are many Y,Z,A,B,C,D waiting in line.
The organisation should not have a policy of come easy go easy for employees.
Specific attempts to retain and encourage employees should be made.
Fresh employees should be special subject of focus to make them comfortable and settled.
You train them,guide them and within 9-18 months they leave making the cycle start again.
By maintaining proper policies of accurate job description,friendly co workers,access to senior officers,attachment to the organisation should be developed in the minds of freshers.
Post induction surveys can be considered.
After say one month meet the new employees and obtain feedback.
HR can play a big role in controlling attrition by bringing put facts,figures,quantified costs of attrition.
After all, employees are the main resources and source of profitability.
Human factor makes lot of difference.
Do you have practise like giving appreciation,get togethers??
Mentor them them,coach them and bring out the best.
Also those employees who will not be a good fit should be given an exit route, as some said "the only thing more expensive than a good developer is a bad developer.