I drill a hole and attach a bolt at the top of my ladders. This makes a great spot to hang an extension cord, tool belt, small bucket, etc. — Mark Ammons
Be sure to use a long bolt and secure it with washers so that a large portion of it sticks out from the top of the ladder, as shown in the photo. Also, some ladders come with premade holes in the top, so you may be able to simply find a bolt that fits and can be secured with washers rather than having to drill another hole.