Mountain Bikes

[Steve85]

As part of my fitness efforts, I'm bringing biking back. Funny that the last post is Christmas related... I am putting a new rear shock for the mountain bike on my list for Mrs. Santa. I need help picking out a new shock to replace the Fox that always needs pumped up and loses pressure quickly. The bike is a Trek Fuel 100 bought off eBay 5-6 yrs ago.

I won't be riding real hard anytime soon but I am what they call in the biking world a clydesfatassdale. The bike seems pretty light for a mtn bike already (I don't have much to compare it too, but it's definitely not heavy) so strength is more important than saving a few ounces here. I doubt I need a ton of tuneability but some adjustment might be helpful. I think I'd like to be able to lock it out completely and ride it as a hardtail if I'm just cruising with the kiddos or something. Not sure what to budget, but if I could stay under $125 and not have it break when I land a small jump or something that would be nice.

Suggestions? Where should I look?