Problems with hair washing

I am new on here and don't know if this topic had sheen covered. Here goes:

My son is now 6 and has been diagnosed with dyspraxia when he was 4 and now awaiting assessment for ASC.

Ever since he was 8 months old, he has had a problem with having his hair washed. now that he is bigger and stronger it is becoming virtually impossible to wash his hair. We have tried a number of different ways including goggles and ear plugs. We have tried to speak with him about this but had no success. We have tried dry shampoo, but it doesn't really clean the hair

Has anyone experienced this and has any suggestions? I would be grateful for any advice