Your point about your work being taken offline or altered after hand-over is important here. Make a habit of including in your contracts that you are permitted

Your point about your work being taken offline or altered after hand-over is important here. Make a habit of including in your contracts that you are permitted to keep a copy of the work for demonstration purposes (where possible) and use that for demonstration. Don't aim to show all of your work. Instead, select your best pieces which demonstrate the depth of your skill for each of the key areas you wish to demonstrate you can do. Select pieces based on the complexity of the project, or the way you approached it. I would recommend including a picture of the site/product as a companion to a succinct description of the technologies and frameworks you used. Include the benefits of the solution you implemented.