Solved by yoshitomo-matsubara in post #2 
              
              
                Hi @anujd9 


Assuming your ssd model is instantiated as model, you should be able to access to the last ReLU layer of its feature_extractor by model.feature_extractor[-1][-1].relu 
By using backward hook function (i.e., register it by model.feature_extractor[-1][-1].relu.register_backward_hook(your…