Not Advertising TRy
Bamert et al.  suggested that V can effectively avoid isolation by not relaying transaction TRy. By doing so, all the neighbors of V will forward TRa to V who will be able to detect the double-spending attack immediately.
This countermeasure can be circumvented if the attacker also similarly does not immediately advertise TRa in the network. As soon as the V advertises TRy (and one of the attacker’s nodes receives it), TRa can be advertised in the network to prevent V from detecting the attack.
Forward First Double-Spend Attempt
In order to efficiently detect double-spending on zero-confirmation transactions, Karame et al. proposed in [1,11] that Bitcoin peers forward transactions that attempt to double-spend the same coins in the Bitcoin network. Namely, whenever a peer receives a new transaction, it checks whether the transaction uses coins that have not been spent in any other transaction that resides in the blockchain and in their memory pool. If so, then peers follow the current protocol of Bitcoin; peers add the transaction to their memory pool and forward it in the network. If, on the other hand, peers detect that there is another transaction in their memory pool that spends the same coins to different recipients, then the peers forward the transaction to their neighbors (without adding the transaction to their memory pools).
To decrease the number of transactions circulating in the Bitcoin network and to prevent the deterioration of the performance of the network, peers can only forward the first double-spending transaction attempt in the network and drop all subsequent double-spending of the same coin. This variant ensures that all peers in the network can identify and verify the misbehaving address and refuse to receive any subsequent transaction from this address. This variant detection technique has been integrated in Bitcoin XT .
Recently, Gervais et al.  showed that the protection of Bitcoin XT is not effective in preventing double-spending attacks of fast payments. They show that A can deny the delivery of double-spending transactions to the merchant using the attack described in Section 4.1.3, thus effectively preventing a Bitcoin XT node from discovering any double-spending attempt.