maintaining sites with constant browser upgrades

hello everyone,
my clients are small business and personal users who sometimes do not
understand that their site may not function tomorrow exactly as it did when
designed a year or more ago. as we all know, what works on one browser
version doesn't necessarily work on a newer version or another browser.

it is impossible to guarantee that a site will function properly for an
unlimited period of time given the constant upgrading of browsers, operating
systems, and coding standards. as many have remarked on these lists, the
newer browsers will often break pages designed for previous versions.

how do you strike that balance between keeping your coding simple enough to
stand the test of time for your clients and if/when your pages do 'break'
due to an upgrade ensuring you do not have to spend hours redesigning a
whole new site for free?

i'm wondering how others deal with the constant changes in regards to
maintaining your web sites, and how you charge for this service if a problem
occurs. ie. billing hourly for changes required to the pages to 'fix' them
for newer browser versions. obviously the best thing to do is to cover this
within a contract.

as always, your expertise is appreciated.
kim

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