Darry certainly tried to keep Ponyboy out of trouble, but was not always successful.
Firstly, by becoming head of the family and keeping his brothers together after the death of their parents, Darry keeps Ponyboy and Soda from going into care and being part of the welfare system. He is also insistent that Ponyboy has someone with him when he is out. This is why Darry is so angry when Ponyboy is 'jumped' outside the cinema in the opening chapter.
Darry is especially hard on Ponyboy - tougher than his parents were in Ponyboy's estimation. This is because Darry is genuinely scared for his brothers and is anxious that they stay safely together.
Darry is very hard on Pony to make sure he dosen't have his life. He dropped out of collage to come and take care of his brothers he wants to make sure Pony grows up smart and happy.