Non deletable visual element

Hello,
Is there any way to make a visual element, specifically a custom node in the graph view non-deletable? I would like to add my custom node when creating the graph and let prevent the user from being able to delete it similar to how the animator prevents you from deleting the entry/any state and exit state nodes.

I know that overriding the IsSelectable method on the node will make it non selectable and so non deletable but I want the user to be able to move it around the graph view. Is there something like an IsDeletable that I can override to achieve what I am trying to do?
Thanks

 

Oh, I didn't know there was such a thing, that is exactly what I was searching for.
Thank you.