You can modify an employee to not accrue any leave, by customising a section known as Leave Allowances.
Please follow these steps to do so:
Navigate into the Employees section
Select the name of the employee
Select Leave Allowances from the left menu
Change the figure listed in the 'Units' field for each type of leave you wish to change
Select Save
This will change the rate of leave accrual for each type of leave that you change. Please note, these changes will only affect future and unlocked pay runs. Any existing pay runs will stay as they are to preserve historical accuracy.