Strength can generally be considered a culmination of several factors including the integrity and strength of the tendons, muscles, and neural conditioning. So if you have built up strong tendons and neural pathways, it should take awhile for it to diminish if you quit working out, but I can’t say exact figures.
Strengthening the connective tissue is a type of strength training. They need lots of rest though, and training it a lot is something you need to be careful with because tendinitis can really set you back. Generally I would say isometrics and negatives are good for this, but honestly any kind of strength training will be helpful. Also pretty much any of the straight arm leverage skills from gymnastics (back lever, human flag, etc) will work the tendons really well. I suppose you could say that anything that requires lots of relative strength.
Anyway, Al may be able to shed more light on this.