Cant get 6 month old baby to fall asleep?

my 6 month old has got into a habit of not going to sleep easily for naps/bedtime. i try to get him to sleep as soon as he looks sleepy as the more tired he is the worse it gets but he just fights it and will spend a long time trying not to be held/rocked to sleep by punching/scratching/pulling hair/wriggling away/screeching/screaming/spitting his dummy out etc and its so exhausting. sometimes it can take an hour to get him to sleep all the time being scratched and hair pulled (hes a very strong baby) and i have to really hold him tightly and rock him a lot to get him to sleep. half the time i give up and let him scream for a while and try again as i have a bad back and he only responds if you stand up (you cant sit down and cuddle him) you cant rock him in a pushchair either as he will scream very loudly. i dont know what to do but it is relly stressing me out and getting me down as it feels like all he does is cry all day and scratch and hit and pull hair/etc. are there any other things i can try so i dont have to go through this all day? (he has lots of short naps so i basically spend the whole day doing this) thanks