Slide master

Hi Kate

Thank you for your question. There isn't a way to lock the slide master but you might try exporting the slide as an picture and then using the picture as the background to your slides.

To try this first set up the master for your presentation and in normal view create a blank slide. From the file menu choose Save as and in the save as type box select jpg. When you click OK PowerPoint asks if you want to export the current or all slides. Choose Current slide only and click OK.

In your presentation switch to the Slide Master view and choose Format > Background. In the dialog box that appears click the drop down arrow and choose Fill Effects. From here select the Picture tab. Click select picture and browse to find your exported slide image. Once selected click OK and apply to all.

Still in Slide Master view remove your original elements which should reveal the picture in the background.

Switch back to normal view and add your slides to the presentation. In future if someone wants to change the elements in the the master they will need to change the underlying picture.

I hope this helps - do let us know if you have any further questions.

Kind regards,
Andrew