Creating An Account to Lend Out

And By that, I mean by the way I see it.

Yesterday, I posted an article on how we can have atomic swap between BTC and Hive. This is important because this way there is nobody who keeps a deposit and nobody who runs away with the deposit. The technique makes it impossible for someone to run away with the Hive dollars or BTC.

So this is concerning the lent out account called C.

This is TX2 as described in my last post:

[
  "account_update",
  {
    "account": "hiveio",
    "posting": {
      "weight_threshold": 1,
      "account_auths": [],
      "key_auths": []
    },
    "owner": {
      "weight_threshold": 1,
      "account_auths":  [],
      "key_auths":[]
    },   
    "active": {
      "weight_threshold": 2,
      "account_auths":  [
         [
           "A",
           1
         ],
         [
           "B",
           1
         ],
      ],
      "key_auths": []
    },
    "memo_key": "STM6FATHLohxTN8RWWkU9ZZwVywXo6MEDjHHui1jEBYkG2tTdvMYo",
    "json_metadata": ""
  }
]

There is nothing A and B cannot do with account C without the consent of the other. But the lender, D, is going to want the account back after the trade so that is why there was TX1:

[
  "account_update",
  {
    "account": "hiveio",
    "posting": {
      "weight_threshold": 1,
      "account_auths": [],
      "key_auths": []
    },
    "owner": {
      "weight_threshold": 1,
      "account_auths":  [["D", 1]],
      "key_auths":[]
    },   
    "active": {
      "weight_threshold": 1,
      "account_auths":  [],
      "key_auths": []
    },
    "memo_key": "STM6FATHLohxTN8RWWkU9ZZwVywXo6MEDjHHui1jEBYkG2tTdvMYo",
    "json_metadata": ""
  }
]

It occurred to me that TX1 could lose its authority should A and B conspire to steal the account. It's easy to do. So now the account lender, called D in the last article, needs to be part of the authorities set up. With a 3-of-3 arrangement D must sign off on all transactions involving the lent out account C.

There is one way D could take his account back early and steal the HBD. Can you think of how this can be done? What changes can be made to the algorithm or requisites can be added to prevent that from happening?