Very low frequency (<1Hz) high pass filter design
It depends on how accurately you are expecting to control your cutoff frequency. A few point come to mind ...


Tolerance


High value electrolytic capacitors have wide tolerances, indeed cheap ones can be as wide as +100%/-50%. You won't get much better than &#177;10% and stability could still be an issue. Solid electrolyte (aluminium/tantalum) have better stability but will be much more expensive.


Leakage


Electrolytic capacitors will have a finite leakage current which will produce dc offsets given that your resistor values will also be high.


Polarization


Make sure that your circuit biasing keeps capacitors correcty polarized.


Charge/Discharge


High value capacitors will have to charge &amp; discharge somehow if there is a non-zero dc bias (ie single rail). This will cause turn-on 'thumps' as the circuit settles-down which may take a many (tens of) seconds. At turn-off, the capacitors may discharge into the op-amp causing damage although given that your resistor values will also be large, this is less likely to be a problem.

The lowest frequency filter I have ever built was a 5Hz &#177;20% two-stage S&amp;K (4 pole) maximally flat design which worked perfectly well.

You might also want to look at a Gyrator circuit to simulate a high value inductor.