Memory usage and memory leaks

Mine is a very big with highly complex C program. I found the program crashes often while running. Even after giving fixes using core-dump analysis it was keep happening, I felt there may be memory releated issues.

First I started to use 'top' command to see the memory usage of this program - keep increasing some time went upto 2Mb for every 15 minutes. But mostly around 150Kb for every 15 minutes and keep increasing for every 15 minutes. Memory used doesn't get reduced at all. I felt it as an indication of memory leak. Then I learnt 'valgrind' and gave fixes (almost 90% issues reported by valgrind).

Now also the memory usage keeps increasing in the same manner as that before giving fixes to memory leaks. My team feels still there are memory leaks. How can I show them that there are no memory leaks (if there is not) or limited and is there relation exists between memory usage and memory leaks?

http://valgrind.org/info/tools.html - say memcheck
http://www.perens.com/works/software/ElectricFence/

If your program is doing something like
- read a file, allocate some memory
- do work
- write a file, free the memory
Then yes, I'd expect it to level off at some point, perhaps increasing every so often in response to a new largest file seen so far scenario.