i use a plugin called MonumentAddons to add further items to monuments, would it be possible to make the lock delete itself on anything placed with this plugin? [i have a large furnace amongst other things in outpost currently]

I think the request here should be, can this plugin prevent placing locks on static entities, such as refineries at monuments. Given that this plugin allows placing locks on them, it creates a potential abuse vector for those entities, regardless of which plugin (or whether a plugin) spawned the entity.

Now having said that, I see in the documentation and the code that this plugin already has some handling of static prefabs, specifically the static BBQ and the static refinery. Rather than prevent placing the locks, it instead deletes the lock afteward, which I suppose is good enough.

@ijks2 Can you please provide a list of specific entities (full prefab path) for which this is an issue? For entities that can appear in vanilla monuments, as well as for non-deployable entities that mappers may place via RustEdit, it would makes sense for this plugin to prevent locking. For entities which players can deploy, which you are placing via Monument Addons, we can address by making Monument Addons disallow placing locks. For deployable entities placed via RustEdit, another solution will be required.

after a bit of messing around i fixed one of the items, now the only one i have inside a monument that can be locked is the Hitching trough [there is no static version from what i could find] 

I pushed a commit to Monument Addons on GitHub which prevents deploying locks on all entities spawned by Monument Addons. I tested and it's compatible with Lock Master. Note: If you happen to reload Lock Master after Monument Addons has spawned the entity, Lock Master will re-enable locking, so you'll need to subsequently reload Monument Addons in that case (shouldn't be an issue generally).