Problem concentrating during Vipassana meditation I am having trouble maintaining concentration for long periods of time. 
I make my breath slightly hard and then pull my mind back to it and then carry on as normal. But it's quite hard to have a long sustained period of breath observation. 
Once maintained I try to move from head to feet taking large body parts such as head, abdomen, arms and legs. Do this for a while and then the mind wanders away again and come back to breath. 

At times the mind wanders for long periods of time until I realise it's wandered away. I haven't been able to penetrate and observe smaller, subtler sensations since a year now. 
I know it's harder to do this at home than at a retreat but I am wondering if this has something to do with my Silas. 

Although they are not the most perfect I do try my best to maintain them. 

Anyone stuck in similar phases and overcame it? Suggestions are welcome. 

Ps. I am a Goenka student and very faithful towards it and have never tried anything else and don't intend to as I am very happy with the results this technique has brought me.
When you breath be mindful of the start to end of the in and out breath. For each breath in and out breath be mindful of whether your mind wandered away during this time. Also note the length of the breath in and out breath. 

When scanning the body keep your concentration anchored on the breath and sensation on the base of the nose as well. If your mind wanders away bring it back to Anapana and then continue the scanning. For each in and out breath see if your mind has wondered away for that period. Also note the sensations that arise when your mind wanders to an alternative object and the sensation when it is with the chosen object.

In some parts stay for a while (but not too long) also focusing on the breath. Sometimes this helps sharpen the mind to see clearly the sensation arising and passing away in the particular section of your body.