1.Go to the dogs–not as successful as in the past(usually used in the continuous tense).

不如过去成功（通常使用进行时）

例句：That company will go bankrupt if it's not careful. It's going to the dogs.

那家公司要是不小心的话就会破产的。它可能会完蛋的。

2.To put the cat among the pigeons – to cause trouble.

惹出乱子

例句：Sending the most unpopular manager to talk to the team was like putting the cat among the pigeons.

把最不受欢迎的经理派去和团队谈话一定会惹出乱子的。