Have they had keys to your house? Are your locks secure, hard to pick?
Invest in good quality locks on doors and windows put on additional bolts and use a door chain when at home.
Do you suspect your stalker is breaking into your home? Think about in-house surveillance.
Today, there are inexpensive cameras you can set-up in your home (think nanny cams). They allow you to login and look at your home using your mobile. Many are motion activated and will record anyone coming into the home.
Are you safe when answering the door?
Install a spyhole, motion detector lights in the front, back and sides and consider an intercom or video intercom (they are no longer very expensive)
Are you safe when you come home?
Have your motion detector light set to come on several feet before you reach your door.
Have a personal alarm and keys ready to use.
Go outside during the day and night and look inside your house what can you see?
Consider using film on the windows to obscure the view.
Close curtains as soon as it starts to be come dusk
Are there any shrubs and bushes where they can hide to watch you?
Cut bushes back or remove them
Use prickly bushes as a barrier against windows.
Are there dark areas where they can lurk?
Consider putting up solar garden lights or a motion detection light not only at your door but at the back and side of the house as well.
If you suspect they are coming around the house, then consider getting a motion detection video camera that for both day and night.
How high is your fence?
You can add height to a fence by adding a trellis, it helps screen the garden without being strong enough to climb.
How can you make the path up to your doors and around the perimeter of the house work for you?
Using gravel, slate or pebbles on driveways and paths will help you hear someone approach.