It's a little dicey using aluminum. You would be soldering a copper based lead in - presumably the center conductor of a length of coax - to aluminum; the dissemilar metals will eventually cause a chemical reaction that would cause problems. There are chemicals, as I understand it, that will allow you to solder and bond copper to aluminum without problems but to be honest I've never had the occasion to use them.
We should also be careful about using the term 'longwire'. A true longwire, such as a Beverage or Vee-beam, are a wavelength or more long, and in the case of the Beverage, can be terminated at the far end with a resistor to make them more uni-directional (the Beverage is bi-directional, more or less right off its ends). What most folks put up are better termed 'random wires' or 'inverted L'; the latter being a length of wire with a lead in coming off the nearest end to the house.
The Vee beam was discussed extensively in books by Bill Orr W6SAI. In them, he describes them as each leg being a wavelength or more long, and fed with ladder line.
All three have their place, just be sure to be clear with the terminology. 73 Mike
The problem, as I mentioned, is that bonding aluminum to copper is dicey without some protection from eventually having 2 dissimilar metals bonded to one another chemically react and destroy the connection. I can't remember the compound's name that you would need to put on to stop this from happening
Beams and verticals are very different animals from HF random wires - they usually use a SO239 type connector and aren't concerned about metal-metal bonding issues.
I've had an aluminum longwire with copper feedline up for almost three years now with no problems at all. As k9rzz said; make sure you have a good clean connection to your feed line and keep it well sealed against the elements.
This is not to say I won't have any problems, in fact I probably just jinxed myself...
Let's condense this into a one word answer; for a thousand reasons it's "no". It wasn't a wise choice for the dog either; in a few years it will be highly corroded and brittle, pretty useless when it falls apart. That cheap aluminium "grounding wire" isn't the same alloy as used for antennas and is pretty useless overall. Electric fences are made with galvanized soft steel wire for a reason, they're durable.