joint supplement for large dogs

My 2 year old cross is competing in agility and we train 2x weekly. Should I be giving him a joint supplement to prevent any problems in the future.

Some green lipped muscle tablets wouldn't hurt and do wonders at both boosting health and keeping joint pains away. 1 a day of the Seatone ones from boots can do wonders.

Theres a brand 'permanax' that is green lipped mussel extract. The way they extract it is diff as it is freeze dried or something like that instead of heat extraction and therefore supposed to be of better quality? they do animal and human supplements. I have never used them but if green lipped muscle extract works (my mother in law swore by ti for her gammy knees) then its poss worth a look at it used by quite a few of the top horse people.