Insert file at Field not Bookmark, how?

[kiln]

I've used fields for merging etc but right now I'm hoping to use them
for more reliable markers for where external docs should be inserted
into a main doc. The bookmarks are too vulnerable to user deletion etc.
I've seen this idea promoted here, but don't really know which field
type would be appropriate to use, etc. Could someone point me to some
sample code? The bookmark code looks like so:

ActiveDocument.Bookmarks("InsertTemplate").Select
Selection.InsertFile FileName:=strPath & strFileName, _
Range:="", ConfirmConversions:=False, _
Link:=False, Attachment:=False